Detecting device and detecting method

ABSTRACT

A detecting device ( 1 ) detects a combustion state of an internal combustion engine ( 2 ) that transmits power via a crankshaft ( 11 ). The detecting device ( 1 ) includes a calculation unit ( 1   b ) that calculates a mass burn fraction by detecting a crank angle, on the basis of a frequency component showing a state change amount of a state change of a detection target according to a change in a cylinder pressure depending on a combustion cycle of the engine ( 2 ), and including a harmonic wave component of a fundamental wave of the frequency component.

CROSS-REFERENCE TO RELATED APPLICATION

This is a Continuation Application of International Application No.PCT/JP2012/063096, filed May 22, 2012, which claims priority to JapanesePatent Application No. 2011-259502 filed on Nov. 28, 2011. The contentsof the aforementioned applications are incorporated herein by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to a detecting device and a detectingmethod that detects the state of an internal combustion engine.

2. Description of Related Art

As measures for realizing low fuel consumption in engines (internalcombustion engines) and realizing clean exhaust gas, an engine controlunit (ECU) is required to correctly detect an engine combustion state toappropriately perform control according to the detected combustionstate. As state variables of the engine combustion state, an indicatedmean effective pressure (hereinafter referred to as IMEP), a heatrelease rate (hereinafter referred to as HR), and a mass burn fraction(hereinafter referred to as MBF), and the like are known. For example,there is a technique showing the engine combustion state depending onIMEP (for an example, refer to Japanese Unexamined Patent Application,First Publication No. 2010-261370). According to this JapaneseUnexamined Patent Application, First Publication No. 2010-261370, atechnique of analytically calculating IMEP is shown, paying attention toa change in cylinder pressure and cylinder volume being periodic.According to this technique, it is shown that IMEP is calculated byoperation processing according to an operational expression including,as variables, the amplitude of a fundamental wave included in a cylinderpressure waveform and the amplitude of a secondary harmonic wave, on thebasis of the fundamental wave having the rotational frequency of acrankshaft as a fundamental frequency.

Additionally, in recent years, it is expected that vehicles or hybridcars be equipped with a function to stop an engine at the time ofvehicle stop, which realizes low fuel consumption and clean exhaust gas.In the vehicles equipped with the function to stop an engine at the timeof vehicle stop, the stop and start of the engine are frequently andrepeatedly performed according to the vehicle stop. Additionally, in thehybrid cars, switching between motor drive and engine drive areperformed during traveling. When the motor drive and the engine driveare switched during traveling, repetition of the stop and start of theengine is frequently performed. In the vehicles that realize low fuelconsumption and clean exhaust gas by the aforementioned switches, theidling state of the engine is reduced and controlled until a stop stateis reached, and thus resulting in engine being restarted.

When the engine of a vehicle starts, the operational state of the enginechanges greatly similar to a case where acceleration or deceleration ofthe vehicle is performed. Therefore, when the engine starts or whenthere is acceleration or deceleration, it is difficult for an enginecontrol unit to appropriately control engine combustion according to theoperational state of the engine.

SUMMARY

Incidentally, to appropriately control combustion of an engine, it maybe necessary to change controlled variables to respective actuators thatcontrol the engine according to crank angle. In calculating the abovecontrolled variables, the combustion state of the engine is detectedfrom the crank angle, and the state variables showing the combustionstate of the engine are calculated by operation processing based on thevarious detected information. Predetermined controlled variables arecalculated in correspondence with the crank angle, on the basis of thecalculated state variables.

However, when the operation processing of calculating the statevariables showing the combustion state of the engine is performed on thebasis of the various kinds of information according to the crank angle,it is necessary to repeatedly perform the operation processing accordingto detection intervals. For example, it is necessary to perform theoperation processing according to respective measurement informationitems detected with the detection intervals being 1 deg. CA (crankangle), on the basis of the above detection intervals. It is possible toapply a method using such operation processing to an engine as anexperimental device. However, when an ECU mounted on an actual vehicleis made to perform such operation processing, the load of the operationprocessing become heavy. Therefore, it is difficult to apply suchoperation processing to engines mounted on general vehicles.

Additionally, to directly detect the cylinder pressure showing thecombustion state of the engine so as to calculate MBF, it is necessaryto provide a special pressure sensor that measures the cylinder pressurein the engine. The aforementioned special pressure sensor requires, forexample, high resistance against high temperature and high pressure.Therefore, since the pressure sensor as described above is generallyexpensive, the sensor is used mainly for experiment. Even if such acylinder pressure measuring method can be applied to the engine as theexperimental device, it is difficult to apply this method to enginesmounted on general vehicles. In this way, even if MBF can be used as anindex showing the combustion state of the engine as the experimentaldevice as an index for controlling an engine, it is not possible to useMBF as an index showing the combustion state of the engines mounted onthe general vehicles.

Meanwhile, according to the technique of Japanese Unexamined PatentApplication, First Publication No. 2010-261370, IMEP is calculated onthe basis of the measurement information detected by the sensor attachedto the outside of an engine combustion chamber. Additionally, IMEP canbe calculated without narrowing the detection intervals of themeasurement information or the intervals of the operation processing ofcalculating the controlled variables, unlike the one described above.However, even if there is a disclosure of the technique of calculatingIMEP in Japanese Unexamined Patent Application, First Publication No.2010-261370, there is no disclosure of a technique of calculating MBF.In this regards, it is difficult to calculate MBF as the index showingthe combustion state of the engine. Additionally, since MBF cannot beeasily calculated from the technique of Japanese Unexamined PatentApplication, First Publication No. 2010-261370, it is also difficult tocalculate MBF according to the crank angle.

The invention has been made in view of such circumstances, and a purposethereof is to provide a detecting device and a detecting method that candetect a crank angle without using a special pressure sensor to therebyeasily calculate a mass burn fraction.

[1] The invention has been made to solve the above-described problems,and is a detecting device that detects a combustion state of an internalcombustion engine that transmits power via a crankshaft. The detectingdevice includes a calculation unit that calculates a mass burn fractionby detecting a crank angle, on the basis of a frequency componentshowing a state change amount of a state change of an detection targetaccording to a change in a cylinder pressure depending on a combustioncycle of the engine, and including a harmonic wave component of afundamental wave of the frequency component.

[2] Additionally, according to the invention, in the above-describedinvention, the frequency component showing the state change amount ofthe state change of the detection target is a frequency componentincluding a harmonic wave component of a fundamental wave having arotational frequency of the crankshaft as a fundamental frequency.

[3] Additionally, according to the invention, in the above-describedinvention, the calculation unit calculates the mass burn fraction on thebasis of a correlation between the harmonic wave component and the crankangle.

[4] Additionally, according to the invention, in the above-describedinvention, the calculation unit calculates the mass burn fraction,using, as the frequency component, a plurality of frequency componentsamong frequency components corresponding to frequencies of naturalnumber multiples of the fundamental frequency or frequencies of (naturalnumber −0.5) multiples of the fundamental frequency.

[5] Additionally, according to the invention, in the above-describedinvention, the calculation unit determines any frequency group out of afrequency group including frequencies of natural number multiples of thefundamental frequency according to a rotation speed of the crankshaftper one combustion cycle of the engine or a frequency group includingfrequencies of (natural number—0.5) multiples of the fundamentalfrequency, and calculates the mass burn fraction, using, as thefrequency component, frequency components corresponding to a pluralityof frequencies among frequency included in the determined frequencygroup.

[6] Additionally, according to the invention, in the above-describedinvention, the calculation unit includes at least one of the frequencycomponents up to the fifth order of the fundamental wave as the harmonicwave component.

[7] Additionally, according to the invention, in the above-describedinvention, the calculation unit includes fourth and fifth frequencycomponents of the fundamental wave as the harmonic wave component.

[8] Additionally, according to the invention, in the above-describedinvention, the calculation unit calculates the mass burn fraction on thebasis of an expression showing a combustion model obtained by modelingthe combustion cycle of the engine, and including, as variables, a firstcrank angle according to a timing of ignition in the combustion cycle ofthe engine, a second crank angle according to a timing of combustion endin the combustion cycle, a third arbitrary crank angle, and a mass burnfraction according to the third crank angle.

[9] Additionally, according to the invention, in the above-describedinvention, a combustion model coefficient inherent in the combustionmodel is included in an element of the expression showing the combustionmodel, and the combustion model coefficient is obtained on the basis ofinformation on a plurality of known sets that are arbitrarily selectedamong information on sets of crank angles and mass burn fractionsaccording to the crank angles, and the calculation unit calculates themass burn fraction according to the expression showing the combustionmodel that is an operational expression including the combustion modelcoefficient in the element.

[10] Additionally, according to the invention, in the above-describedinvention, the plurality of known sets that are arbitrarily selected arethree sets, a relationship between the respective crank angles of thethree sets, and the first crank angle according to the timing of theignition is represented by Expression (1), and the plurality of knownsets are selected so that the relationship between Z of Expression (1)becomes any of 0.5, or 1, 2 and 3.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 1} \right\rbrack & \; \\{\left( \frac{\theta_{{MBF}\; 2} - \theta_{s}}{\theta_{{MBF}\; 3} - \theta_{s}} \right)^{Z} = \left( \frac{\theta_{{MBF}\; 1} - \theta_{s}}{\theta_{{MBF}\; 2} - \theta_{s}} \right)} & (1)\end{matrix}$

θ_(MBF1), θ_(MBF2), and θ_(MBF3): Crank angles that constitute a set ofan arbitrary crank angle and a mass burn fraction according to the crankangle are given in three different sets

θ_(s): First crank angle according to the timing of ignition

[11] Additionally, according to the invention, the above-describedinvention, the detecting device further includes a control unit thatcontrols an operational state of the internal combustion engine on thebasis of the calculated mass burn fraction.

[12] Additionally, the detecting method of the invention is a detectingmethod that detects a combustion state of an internal combustion enginethat transmits power via a crankshaft. The detecting method includes aprocess of calculating a mass burn fraction by detecting a crank angle,on the basis of a frequency component showing a state change amount of astate change of a detection target according to a change in a cylinderpressure depending on a combustion cycle of the engine, and including aharmonic wave component of a fundamental wave of the frequencycomponent.

As described above, according to the invention, it is possible to detectthe crank angle without using a special pressure sensor to therebyeasily calculate the mass burn fraction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an engine control unit and an engineaccording to an embodiment of the invention.

FIG. 2 is a schematic view (1) showing the positions of sensors in acylinder structure in the present embodiment.

FIG. 3 is a schematic view (2) showing the positions of the sensors inthe cylinder structure in the present embodiment.

FIG. 4 is a view showing the states of combustion parameters from startto a steady operation.

FIG. 5A is a view showing the states of the combustion parameters fromthe start to the steady operation, which are classified into groupsaccording to a combustion state.

FIG. 5B is a view showing the states of the combustion parameters fromthe start to the steady operation, which are classified into the groupsaccording to the combustion state.

FIG. 5C is a view showing the states of the combustion parameters fromstart to the steady operation, which are classified into the groupsaccording to the combustion state.

FIG. 5D is a view showing the states of the combustion parameters fromstart to the steady operation, which are classified into the groupsaccording to the combustion state.

FIG. 6A is a view showing combustion images captured in synchronizationwith measurement of cylinder pressure.

FIG. 6B is a view showing combustion images captured in synchronizationwith the measurement of the cylinder pressure.

FIG. 6C is a view showing combustion images captured in synchronizationwith the measurement of the cylinder pressure.

FIG. 6D is a view showing combustion images captured in synchronizationwith the measurement of the cylinder pressure.

FIG. 7 is a view showing HR and MBF corresponding to the combustionimages shown in FIGS. 6A to 6D.

FIG. 8 is a view showing the relationship between the amplitude of afundamental wave and MBF timing θ_(MBF) at the start time.

FIG. 9 is a view showing the relationship between the amplitude of asecondary harmonic wave and the MBF timing θ_(MBF) at the start time.

FIG. 10 is a view showing the relationship between the amplitude of athird harmonic wave and the MBF timing θ_(MBF) at the start time.

FIG. 11 is a view showing the relationship between the amplitude of afourth harmonic wave and the MBF timing θ_(MBF) at the start time.

FIG. 12 is a view showing the relationship between the amplitude of afifth harmonic wave and the MBF timing θ_(MBF) at the start time.

FIG. 13 is a view showing the correlation between a harmonic wave orderk and the MBF timing θ_(MBF) at the start time.

FIG. 14 is a view showing P_(max), θ_(Pmax), and IMEP calculated fromthe cylinder pressure measured during an acceleration/decelerationoperation.

FIG. 15 is a view showing changes in ignition delay, combustionduration, and IMEP during acceleration/deceleration operation duration.

FIG. 16 is a view showing the results obtained when the cylinderpressure P, HR, and MBF in a complete cycle during accelerationoperation duration are overwritten.

FIG. 17 is a view showing the results obtained when the cylinderpressure P, HR, and MBF in the complete cycle during constant-speedoperation duration are overwritten.

FIG. 18 is a view showing the results obtained when the cylinderpressure P, HR, and MBF in the complete cycle during decelerationoperation duration are overwritten.

FIG. 19 is a view showing a combustion pattern Gr.11 from which twopeaks can be observed in the cylinder pressure P.

FIG. 20 is a view showing a combustion pattern Gr.12 in whichfluctuations in patterns of a cylinder pressure waveform, a heat releaserate HR, and MBF are small and from which one peak can be observed inHR.

FIG. 21 is a view showing a combustion pattern Gr.12′ from which a flatportion can be observed in the cylinder pressure P after TDC.

FIG. 22 is a view showing the results obtained when the mass burnfraction MBF is approximately identified by the Wiebe function.

FIG. 23 is a view showing the relationship between a coefficient m ofthe Wiebe function, and crank angles θ_(MBF) 0.3, θ_(MBF) 0.5, andθ_(MBF) 0.7 at which the mass burn fraction MBF of Expression (5) shows30%, 50%, and 70%.

FIG. 24 is a view showing the relationship between the amplitude of afundamental wave and MBF timing θ_(MBF) during theacceleration/deceleration operation.

FIG. 25 is a view showing the relationship between the amplitude of asecondary harmonic wave and the MBF timing θ_(MBF) during theacceleration/deceleration operation.

FIG. 26 is a view showing the relationship between the amplitude of athird harmonic wave and the MBF timing θ_(MBF) during theacceleration/deceleration operation.

FIG. 27 is a view showing the relationship between the amplitude of afourth harmonic wave and the MBF timing θ_(MBF) during theacceleration/deceleration operation.

FIG. 28 is a view showing the relationship between the amplitude of afifth harmonic wave and the MBF timing θ_(MBF) during theacceleration/deceleration operation.

FIG. 29 is a view showing the correlation between a harmonic wave orderk and the MBF timing during the acceleration/deceleration operation.

FIG. 30 is a view showing the slope of the MBF timing θ_(MBF) to theamplitudes of frequency components during the acceleration/decelerationoperation.

FIG. 31 is a view showing the relationship between the amplitude b₂ ofthe secondary harmonic wave and MBF timing θ_(MBF) 0.5 at the time ofthe acceleration/deceleration operation and the start.

FIG. 32 is a view showing a case where the number of data items, such asthe cylinder pressure, is reduced, in the calculation of b₂ during theacceleration/deceleration operation.

FIG. 33 is a schematic view showing the positions of the sensors in thecylinder structure in the present embodiment.

FIG. 34 is a view showing the results the cylinder pressure P, HR, andMBF calculated on the basis of output signals of an acceleration sensor,and the cylinder pressure P, HR, and MBF obtained by a digitalcompression sensor are overwritten.

FIG. 35 is a view showing the relationship between the amplitude b₂ ofthe secondary harmonic wave and a maximum cylinder pressure P_(max).

FIG. 36 is a view showing the relationship between the amplitude b₂ ofthe secondary harmonic wave included in the output waveform of theacceleration sensor, and θ_(MBF0.05), θ_(MBF0.25), and θ_(MBF0.80)obtained by the output of the digital compression sensor.

FIG. 37 is a view showing the correlation between MBF obtained on thebasis of b_(k) derived from a sine function, and actual MBF.

FIG. 38 is a view showing the correlation between MBF obtained on thebasis of a_(k) derived from a cosine function, and the actual MBF.

DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of the invention will be described withreference to the drawings. In addition, in the following description,common constituents will be designated with the same reference numerals.

An engine control unit in the present embodiment can detect a crankangle to thereby easily calculate a mass burn fraction. In the followingdescription, a crank angle at which the above mass burn fraction reachesa predetermined value may be referred to as “MBF timing θ_(MBF)”.

(Configuration of Engine and Control Unit Thereof in Present Embodiment)

FIG. 1 is an overall block diagram of an engine and a control unit(engine control unit) thereof in the present embodiment.

The engine control unit (hereinafter referred to as “ECU”) 1 includes aninput interface 1 a that receives data sent from respective sections ofa vehicle (not shown), a CPU 1 b (control unit) that executes operationfor controlling the respective sections of a vehicle, a memory 1 chaving a read-only memory (ROM) and a random access memory (RAM), and anoutput interface 1 d that sends control signals to the respectivesections of the vehicle. Programs and various data for controlling therespective sections of the vehicle are stored in the ROM of the memory 1c. The programs for controlling the engine shown in the presentembodiment are stored in the ROM. The ROM may be a rewritable ROM, suchas an EPROM. A working area for the operation by the CPU 1 b is providedin the RAM. The data sent from the respective sections of the vehicleand the control signals to be delivered to the respective sections ofthe vehicle are temporarily stored in the RAM.

The processing to be performed by the ECU 1 will be described below indetail.

The engine 2 (internal combustion engine) is, for example, a four-cycleengine. The engine 2 is connected to an intake pipe 4 via an intakevalve 3, and is connected to an exhaust pipe 6 via an exhaust valve 5.The intake pipe 4 is provided with a fuel injection valve 7 that injectsfuel according to a control signal from the ECU 1. The exhaust pipe 6 isprovided with an exhaust gas recirculation device (EGR) 22 that shunts aportion of exhaust gas and returns the exhaust gas to an intake system(intake pipe 4), according to a control signal from the ECU 1. The EGR22 includes various sensors (not shown) for EGR control. Intake pipepressure PB detected by the various sensors is sent to the ECU 1.

The engine 2 sucks an air-fuel mixture of the air sucked from the intakepipe 4 and the fuel injected from the fuel injection valve 7 to acombustion chamber 8. The combustion chamber 8 is provided with anignition plug 9 that causes sparks according to an ignition timingsignal from the ECU 1. The air-fuel mixture is combusted by the sparksemitted from the ignition plug 9. The volume of the air-fuel mixture isincreased by the combustion, and this pushes the piston 10 downward. Thereciprocating motion of the piston 10 is converted into the rotationalmotion of a crankshaft 11.

The engine 2 is provided with a crank angle sensor 17. The crank anglesensor 17 sends a CRK signal and a TDC signal, which are pulse signals,to the ECU 1 with the rotation of the crankshaft 11. The CRK signal is apulse signal to that is outputs at a predetermined crank angle (15degrees in this embodiment). The ECU 1 calculates an rotation speed NEof the crankshaft 11 in the engine 2 according to the CRK signal. TheTDC signal is a pulse signal output at a crank angle related to the TDCposition of the piston 10.

The intake pipe 4 of the engine 2 is provided with a throttle valve 18.The opening degree of the throttle valve 18 is controlled by the controlsignal from the ECU 1. A throttle valve opening degree sensor (θTH) 19connected to the throttle valve 18 sends an electrical signal accordingto the opening degree of the throttle valve 18 to the ECU 1.

An intake pipe pressure (PB) sensor 20 is provided on the downstreamside of the throttle valve 18. The intake pipe pressure PB detected bythe PB sensor 20 is sent to the ECU 1.

An air flow meter (AFM) 21 is provided upstream of the throttle valve18. The air flow meter 21 detects the volume of air that passes throughthe throttle valve 18, and sends the air volume to the ECU 1.

An accelerator pedal opening degree sensor (AP) 25 is connected to theECU 1. The accelerator pedal opening degree sensor 25 detects theopening degree of an accelerator pedal, and sends the opening degree tothe ECU 1.

In the engine 2 in the present embodiment, a cylinder structure 2A (FIG.2) is formed by a cylinder block 34, and a cylinder head 35 formed so asto cover an upper portion (upper side in the drawing) of a cylinder.

A cylinder head 35 is provided with a sensor unit 16. The sensor unit 16indirectly detects a change in the cylinder pressure of a predeterminedcylinder of the engine 2, and sends the change to the ECU 1. Forexample, the sensor unit 16 is a gap sensor that detects the deformationvolume of the cylinder head 35.

Additionally, although not shown, the engine 2 can include a mechanismthat variably drives the phase and lift of the intake valve and/or theexhaust valve, a mechanism that makes the compression ratio of thecombustion chamber variable, a mechanism that adjusts intake pressure,or the like.

The signals sent toward the ECU 1 are processed by the input interface 1a. The input interface 1 a performs analog-to-digital conversion of thesent signals. The CPU 1 b processes the converted digital signalsaccording to the programs stored in the memory 1 c, and creates controlsignals to be sent to actuators of the vehicle. The output interface 1 dsends the control signals to the actuators of the fuel injection valve7, the ignition plug 9, the throttle valve 18, the EGR 22, and the othermachine elements.

The detection of the behavior of the cylinder structure 2A will bedescribed with reference to FIGS. 2 and 3, taking a case where theinvention is applied to a single cylinder type engine (single cylinderengine) as an example.

FIGS. 2 and 3 are schematic views showing the positions of sensors inthe cylinder structure. FIG. 2 shows a cross-section of the cylinderstructure 2A, and FIG. 3 shows a plan view of the cylinder structure 2Aviewed from a cylinder head 35 side. The arrangement of the sensor unit16 shown in FIG. 2 is shown as an example.

As shown in FIG. 2, the cylinder structure 2A is provided with thesensor unit 16 that detects the behavior of the cylinder structure 2A.The cylinder structure 2A is obtained by combining the cylinder block 34and the cylinder head 35, and the cylinder block 34 and the cylinderhead 35 are fastened to each other with bolts 37 and nuts 38 with agasket 36 interposed therebetween.

Additionally, an upper portion of the cylinder head 35 is provided withan anchor block 39, and the anchor block 39 is fastened to the cylinderhead 35 with the aforementioned bolts 37 and nuts 38. The anchor block39 is provided with the sensor unit 16, and the sensor unit 16 is heldby the anchor block 39 in a state where a gap of predetermined spacingis maintained between the sensor unit 16 and the cylinder head 35.

As shown in FIG. 3, the position of the sensor unit 16 is provided so asto become the position of the combustion chamber in a state where thecylinder head 35 is viewed in a plan view.

Here, the sensor unit 16 is a sensor that detects the behavior of thecylinder structure 2A. For example, the sensor unit 16 detects thebehavior of the cylinder structure 2A, that is, a force acting on thecylinder structure 2A, gaps, acceleration, the deformation of thecylinder structure 2A, or the like. The cylinder pressure changes infour strokes of intake, compression, explosion, and exhaust of one cycleof the engine 2. A stress or gap change, the acceleration, and thedeformation in the cylinder structure 2A are caused according to achange in the cylinder pressure, a correlation is present among thechange in the stress or gap and changes in respective physicalquantities showing the acceleration and the deformation, in the cylinderstructure 2A, and the change in the cylinder pressure.

According to an example shown in FIG. 2, minute displacement is causedon the surface of the cylinder head 35 due to the change in the cylinderpressure by a combustion cycle. By adopting such a configuration, thesensor unit 16 detects the minute displacement of the surface of thecylinder head 35 as a change in the spacing between the sensor unit 16and the cylinder head 35.

In the ECU 1, the input interface 1 a performs input processing of adetection signal detected by the sensor unit 16, and obtains a signalrelated to a stroke cycle. Additionally, the CPU 1 b performs operationprocessing of the signal related to the above stroke cycle, andcalculates a cylinder pressure instantaneous value, an indicated meaneffective pressure, and the crank angle at which the mass burn fraction,as the state variables showing the combustion state of the engine 2.

In addition, the sensor unit 16 is not limited to that shown in FIGS. 1to 3. Additionally, the attachment position of the sensor unit 16 is notlimited to that shown in FIGS. 1 to 3.

For example, as types of behavior that occurs in the cylinder structure2A that is a detection target, for example, there are a change in thestress in the cylinder structure 2A, a change in the gap between thecylinder block 34 and the cylinder head 35, a change in the gap of thegasket 36 between the cylinder block 34 and the cylinder head 35, achange in the acceleration acting on the cylinder structure 2A, anddeformation in the cylinder structure 2A.

As a more specific example, a sensor unit 16 (a pressure sensor) thatdetects the stress of a detection target, may be made to correspond toeach detection target and be provided at any of the bolts 37 thatfastens the cylinder block 34, the gasket 36, and the cylinder block 34and the cylinder head 35. The sensor unit 16, which is a sensorincluding, for example, a piezoelectric device, generates a cylinderpressure signal according to the cylinder pressure in the combustionchamber 8, and sends the signal to the ECU 1.

Additionally, a sensor unit 16 (a gap sensor) that detects the gapbetween the cylinder block 34 and the cylinder head 35 may be providedat the gap between the cylinder block 34 and the cylinder head 35. A gapsensor for detecting the gap of the gasket 36 may be provided at the gapof the gasket 36.

Additionally, a sensor unit 16 (an acceleration sensor) that detectsvibration in the cylinder block 34 as the acceleration may be providedat the cylinder block 34, and an acceleration sensor that detects theacceleration acting on the cylinder head 35 may be provided at thecylinder head 35.

Additionally, a sensor unit 16 (a gap sensor, a strain detection sensor)that detects the deformation of the cylinder structure 2A may beprovided at the cylinder structure 2A.

The aforementioned respective sensors may be used independently, may beused in combination with other sensors, or may be selectively used ifnecessary.

In addition, although the engine shown in this drawing is a singlecylinder type engine, a multi-cylinder type engine is also applicable tothe present embodiment. Additionally, although this engine is a sidevalve type engine, the detecting method of the present embodiment is notlimited by the arrangement of the engine valve.

(Calculation Formula of Indicated Mean Effective Pressure, Heat ReleaseRate, and Mass Burn Fraction)

Here, the calculation of the indicated mean effective pressure (IMEP),the heat release rate (HR), and the mass burn fraction (MBF), which areknown as the state variables showing the combustion state of the engine,is shown.

First, a technique of analytically obtaining IMEP, paying attention tochanges in the cylinder pressure and cylinder volume being periodic,will be simply described. When a fundamental frequency is used as therotational frequency of the crankshaft, IMEP can be calculated accordingto Expression (2) and Expression (3) by defining the amplitude of afundamental wave included in a cylinder pressure waveform as b₁ anddefining the amplitude of a secondary harmonic wave as b₂ (for details,refer to Japanese Unexamined Patent Application, First Publication No.2010-261370). Specifically, in the case of an engine in which thecrankshaft 11 is operated at 6000 rpm as the rotation speed NE thereof,an amplitude in which b₁ is a 100 Hz component and b₂ is a 200 Hzcomponent is obtained. The frequency of b₁ and b₂ changes depending onthe rotation speed NE of the crankshaft 11. IMEP can be calculated byoperation processing based on the output of a sensor that is attached tothe outside of the combustion chamber of the engine and detects stress,strain, displacement, acceleration, or the like.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 2} \right\rbrack & \; \\{{IMEP} = {\frac{\pi}{2h}\left( {b_{1} + {\frac{1}{2\lambda}\left( {1 + \frac{1}{4\lambda^{2}}} \right)b_{2}}} \right)}} & (2) \\\left\lbrack {{Expression}\mspace{14mu} 3} \right\rbrack & \; \\{b_{k} = {\frac{2}{n}{\sum\limits_{j = 1}^{n}{P_{j}\sin \; \frac{2\pi \; {kj}}{nh}}}}} & (3)\end{matrix}$

b_(k): Amplitude of k-th harmonic wave included in cylinder pressure P(Fundamental wave when k=1)

h: Cycle coefficient (4 cycle h=½, 2 cycle h=1)

n: Number of data items of cylinder pressure of one cycle

j: Data number

λ: Connecting rod stroke ratio (length of connecting rod/radius ofcrank)

Additionally, HR is calculated as a value per unit stroke volume (V_(s):stroke volume) according to the following Expression (4) from a cylinderpressure P and a combustion volume V detected at every 1 deg. CA on thebasis of the crank angle.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 4} \right\rbrack & \; \\{{HR}_{i} = {\frac{1}{\kappa - 1}\left( {{V_{i}\frac{P_{i + 1} + P_{i - 1}}{2}} + {\kappa \; P_{i}\frac{V_{i + 1} + V_{i - 1}}{2}}} \right)\frac{1}{V_{s}}}} & (4)\end{matrix}$

In the above Expression (4), shifting is made as a whole and anatmospheric pressure position is corrected so that polytropiccompression is obtained between BTDC 100 deg. CA to 65 deg. CA. In thecase of the present embodiment, a polytropic index is κ=1.32.

MBF is calculated by substituting HR calculated by Expression (4) intoExpression (5).

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 5} \right\rbrack & \; \\{{MBF}_{i} = {\sum\limits_{j = s}^{i}{{HR}_{i}/{\sum\limits_{j = s}^{e}{HR}_{i}}}}} & (5)\end{matrix}$

k: Polytropic index

i, j: Data number

s, e: Combustion start, combustion end (Duration in which HR remains asa positive value continuously)

As resolving power in the aforementioned calculation method of HR andMBF, it is required that values are obtained at every 1 deg. CA.Therefore, to detect the combustion state of the engine that changesevery moment according to the above-described calculation method,calculation is continuously required at every 1 deg. CA. Additionallythe maximum heat release rate HR_(max), the crank angle θ_(HRmax), andthe MBF timing θ_(MBF) are required to perform operation processing bysecondary interpolation. The same applies for the maximum cylinderpressure P_(max) and the crank angle θ_(Pmax).

However, the above Expression (4) and Expression (5) are used for thedescription of the following principle.

Additionally, in the calculation of MBF, it is also possible to usea_(k) represented by the total of the product of the cylinder pressureand a cosine function as in the following Expression (3)′ as theamplitude of a k-th harmonic wave instead of using b_(k) represented bythe total of the product of the cylinder pressure and a sine functionbeing used as the amplitude of the k-th harmonic wave as the aboveExpression (3).

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 6} \right\rbrack & \; \\{a_{k} = {\frac{2}{n}{\sum\limits_{j = 1}^{n}{P_{j}\cos \; \frac{2\pi \; {kj}}{nh}}}}} & (3)^{\prime}\end{matrix}$

[Study of Combustion Characteristics from Start to Steady Operation]

(Principle of Detecting MBF Timing θ_(MBF))

Changes in the combustion state from start to the steady operation willbe described with reference to FIGS. 4 to 7.

First, a verification experiment performed for describing the principlein the present embodiment will be described.

To capture combustion images for this verification experiment, a glassengine is used in which a portion of the piston 10 is formed of a glassmaterial serving as an observation window. In various types ofmeasurement shown below, measured is the duration until IMEP settles atan approximately constant value while increasing after ignition startand firing from motoring in a state where the opening degree of thethrottle valve 18 is full-open and the rotation speed NE (crank rotationspeed) of the crankshaft 11 is fixed to 1000 rpm. Specifically, theduration in which the measurement is performed is duration up to firstfifty cycles including the motoring, and this duration is used as thestart duration of the engine.

The cylinder pressure is measured at intervals of 1 deg. CA insynchronization with a crankshaft rotation angle by a pressure sensor(not shown) and a charge amplifier (not shown) that are provided at thecombustion chamber 8 for the experiment. The fuel is supplied from thefuel injection valve attached to the intake pipe, and the injectionduration thereof is adjusted to set A/F (air-fuel ratio). A/F used as areference is 15, and ignition timing is BTDC 20 deg. CA.

Additionally, the capturing of the combustion images (FIGS. 6A to 6D) isperformed in sixteen continuous cycles from the ignition start at aspeed of 6500 fps (frame per second) at every 1 deg. CA insynchronization with the measurement of the cylinder pressure, in abottom view from a glass piston side using a high-speed camera.

FIG. 4 is a view showing the states of combustion parameters from startto the steady operation.

Changes in the combustion parameters (vertical axis) due to respectivecycles (horizontal axis) from the start to the steady operation areshown in FIG. 4. Cycle number (No) shown on the horizontal axisrepresents the number of cycles in the case of a four-cycle engine thathas two rotations of the crankshaft 11 as one cycle. Additionally, asthe combustion parameters shown on the vertical axis, the maximumcylinder pressure P_(max); the crank angle θ_(Pmax), IMEP, the maximumheat release rate HR_(max) corresponding to the maximum cylinderpressure P_(max); and the crank angle θ_(HRmax) corresponding to themaximum heat release rate HR_(max) are shown.

The state up to Cycle No. 4 in which IMEP takes negative values is amotoring state. A firing state is brought about in Cycle No. 5, andthereafter, shift is made to the steady operation in which IMEP settlesat an approximately constant value while increasing. Both of P_(max) andHR_(max) increase as the cycles proceed. On the other hand, θ_(Pmax) isretarded up to a value immediately before reaching a predetermined valuein the steady operation, and settles in a range of the predeterminedvalue in the operation in a place slightly returned from a maximumretard angle to a top dead center (TDC) side if entry into the steadyoperation is allowed. θ_(HRmax) reaches the predetermined value in thesteady operation when advance is performed monotonously from the start.

Here, the combustion state at the start time is classified into groups,on the basis of changes (combustion patterns (HR and MBF patterns)) inthe combustion parameters at the start time. Here, the combustion stateis classified into four groups, and the classified groups are designatedas Group 0 to Group 3, respectively, and are represented like Gr.0 toGr.3, respectively.

FIGS. 5A to 5D are views showing the states of the combustion parametersclassified into respective groups of Gr.0, Gr.1, Gr.2, and Gr.3according to the combustion state.

Changes in the combustion parameters (vertical axis) from the crankangle (horizontal axis) are shown in FIGS. 5A to 5D. As the combustionparameters shown on the vertical axis, the cylinder pressure P, HR, andMBF are shown.

Group 0 (Gr.0) shown by FIG. 5A is grouped at the time of the motoring.

Group 1 (Gr.1) shown by FIG. 5B is obtained by grouping first threecycles after the start of the firing. According to a combustion patternshown in FIG. 5B, a maximum value (P_(max)) of P is approximately equalto motoring pressure, and a maximum value (HR_(max)) of HR is small.

Group 2 (Gr.2) shown by FIG. 5C is grouped between Cycle Nos. 8 to 23after Gr.1. According to a combustion pattern shown in FIG. 5C, acombustion state in a cycle in which the peak of HR is one is shown.

Group 3 (Gr.3) shown by FIG. 5D is obtained by grouping Cycle No. 24 andits subsequent cycles corresponding to the second half of the steadyoperation state. According to a combustion pattern shown in FIG. 5D, therate of change of MBF that increases monotonously changes, and a patternhaving a hump in the middle of the graph is formed. A combustion statewhere peaks of HR are two is brought about in a state where such apattern of MBF is detected.

For example, in the case of the engine shown in the present embodiment,sequential changes from Gr.0 of motoring to Gr.3 are made from the startto the steady operation. In this process, rising of HR to the crankangle becomes steep, HR_(max) becomes large, and θ_(HRmax) indicatingthe position of HR_(max) moves toward the TDC side. The cylinderpressure P approaches TDC according to the movement of the pattern of HRtoward to the TDC side, the peak value P_(max) becomes high, andθ_(Pmax) showing the position of P_(max) tends to approach TDC.

Next, the combustion images captured in synchronization with themeasurement of the cylinder pressure will be described with reference toFIGS. 6A to 6D and FIG. 7.

FIGS. 6A to 6D are views showing the combustion images captured insynchronization with the measurement of the cylinder pressure. Threecombustion images with different timings in the same cycle are shown inFIGS. 6A to 6D, respectively.

Additionally, FIG. 7 is a view showing HR and MBF according to thecombustion images shown in FIGS. 6A to 6D.

FIG. 6A shows combustion images immediately after the start of thefiring, and corresponds to the combustion state of Gr.1. Althoughpropagation of blue flames by ignition can be confirmed from thecombustion image at the timing of TDC, the area thereof is small and MBFat this time is 0.6%. If ATDC 10 deg. CA is brought about, the blueflame occupies about 60 percent of the observation window, but MBF is5.8%. Gr.1 is characterized by combustion in which P_(max) isapproximately equal to the motoring pressure as mentioned above andHR_(max) is also small. The above combustion images support this.

FIGS. 6B to 6D are combustion images of the combustion state of Gr.2until IMEP reaches a steady-state value while increasing slowly afterIMEP abruptly increases through firing. FIG. 6B (Cycle No. 12) and FIG.6C (Cycle No. 8) of these take the approximately same IMEP values asshown in these drawings. Nevertheless, the combustion images of FIGS. 6Band 6C are greatly different from each other. It can be understood thatthe combustion images of FIG. 6C have a wider flame area compared to thecombustion images of FIG. 6B even at the same crank angle.

This, as shown in FIG. 7, also corresponds to the rising timing of HR,and the ignition delay in Cycle No. 8 (FIG. 6C) is shorter than that inCycle No. 12 (FIG. 6B). As a result, P_(max) and the variation (dP/dθ)of P to the crank angle θ in No. 8 (FIG. 6C) becomes greater those inCycle No. 12 (FIG. 6B) (Cycle No. 8 (FIG. 6C)>No. 12 (FIG. 6B)).Moreover, a second item b₂ of a right-hand side of an operationalexpression (Expression (2)) that calculates IMEP becomes greater inCycle No. 8 (FIG. 6C) than in No. 12 (FIG. 6B) (Cycle No. 8 (FIG.6C)>No. 12 (FIG. 6B)).

Here, since combustion is retarded as a whole from the relationship inwhich θ_(MBF)0.5 becomes smaller in No. 8 (FIG. 6C) than in Cycle No. 12(FIG. 6B) (Cycle No. 8 (FIG. 6C)<No. 12 (FIG. 6B)), the cylinderpressure P also becomes smaller in No. 8 (FIG. 6C) than in Cycle No. 12(FIG. 6B) after ATDC 50 deg. CA (Cycle No. 8 (FIG. 6C)<No. 12 (FIG.6B)). The above relationship becomes a cause by which a first item b₁ ofthe right-hand side of the operational expression (Expression (2)) thatcalculates IMEP becomes smaller in No. 8 (FIG. 6C) than in Cycle No. 12(FIG. 6B) (No. 8 (FIG. 6C)<No. 12 (FIG. 6B)). From the above, when flamepropagation speed is slow, b₁ increases (b₁→increase), b₂ decreases(b₂→decrease), and when the flame propagation speed is fast, b₁decreases (b₁→decrease) and b₂ increases (b₂→increase). In this way, astate where the IMEP values become approximately equal to each other bythe balance of both b₁ and b₂ is produced.

Meanwhile, in FIG. 6D, a flame occupies about ¼ of the observationwindow in TDC, and if ATDC 10 deg. CA is brought about, an aspect inwhich the flame propagates to the outside of the observation window isimagined. ATDC 20 deg. CA at which the whole image is brightapproximately corresponds to the crank angle θ_(HRmax) at which the heatrelease rate becomes the maximum.

From the above combustion images and combustion analysis results, therelationship between b₁ and b₂ in the operational expression of IMEP isarranged as the following relationships.

When the flame propagation speed is relatively fast, (A) HR risessharply (the rate of change of HR becomes large). Additionally, in theabove case, (B) HR_(max) that is a peak value of HR becomes large.Additionally, in the above case, (C) a position (crank angle) indicatingthe peak of HR approaches TDC. Additionally, in the above case, (D)P_(max), dP/dθ, and b₁ and b₂ become large, respectively. In short, itis shown that the patterns of HR and MBF have any influence on frequencycomponents includes in a waveform (cylinder pressure waveform) showing achange in the cylinder pressure according to the tendencies shown theabove (A) to (D).

(Relation Between Amplitude of Frequency Component of Cylinder PressureWaveform, and Crank Angle at which MBF Becomes Predetermined Value)

Next, the relationship between the amplitudes of frequency components ofa cylinder pressure waveform and a crank angle (MBF timing θ_(MBF)) atwhich MBF becomes a predetermined value will be described with referenceto FIGS. 8 to 12.

In the following description, for example, MBF at which the crank anglereaches 30% is represented as θ_(MBF)0.3. Additionally, θ_(MBF)0.3corresponding to the ignition timing, θ_(MBF)0.7 corresponding to theend timing of combustion duration, and θ_(MBF)0.5 according tointermediate timing between the ignition timing and the end timing ofthe combustion duration and corresponding to the end timing of the firsthalf of the combustion duration is selected as central values of the MBFtiming θ_(MBF).

First, FIG. 8 is a view showing the relationship between the amplitudeb₁ (the fundamental wave amplitude b₁ of the first item of theright-hand side of the IMEP operational expression (the aforementionedExpression (2))) (horizontal axis) of the fundamental wave and the MBFtiming θ_(MBF) (vertical axis), at the start time. Numbers attached topolygonal line graphs showing respective MBF timings θ_(MBF) shown inFIG. 8 are cycle numbers. As the cycle numbers increase (as the cyclesproceeds), a state shifts in the direction of an arrow shown in FIG. 8.According to the direction of the arrow shown in FIG. 8, a tendency inwhich b₁ increases and θ_(MBF) decreases is shown. Additionally, in theduration (from Gr.2 to Gr.3) excluding Gr.1 immediately after the startof the firing shown in FIG. 8, there is little change in the amplitudeb₁ of the fundamental wave. Additionally, in this duration, thecorrelation between b₁ and θ_(MBF) is low. In addition, a b_(k) position(in this case, b₁) when the combustion images shown in theaforementioned FIGS. 6A to 6D are captured is written in this drawing.The same applies for the following views.

Next, the relationship between the amplitude of the secondary harmonicwave and MBF timing θ_(MBF) (vertical axis) at the start time will bedescribed with reference to FIG. 9.

FIG. 9 is a view showing the relationship between the amplitude b₂ (thefundamental wave amplitude b₂ of the second item of the right-hand sideof the IMEP operational expression (the aforementioned Expression (2)))(horizontal axis) of the secondary harmonic wave and the MBF timingθ_(MBF) (vertical axis), at the start time. It can be understood frompolygonal line graphs of the MBF timing θ_(MBF) shown in FIG. 9 thatthere is a tendency different from the aforementioned FIG. 8. In FIG. 9,a range (the range of Gr.2 distributed in a range where b₁ is equal toor more than 160) where, in the aforementioned FIG. 8, the polygonalline graphs of the MBF timing θ_(MBF) overlap each other and distinctionis difficult, spreads in the direction of the horizontal axis and thecorrelation with θ_(MBF) is clear. Additionally, the classification ofthe combustion patterns are allowed on the basis of the magnitude of b₂.

For example, two threshold values (20 kPa and 120 kPa) that determinethe magnitude of b₂ are determined, and the groups of the combustionpatterns are determined on the basis of the magnitude of b₂. When arange of b₂<20 kPa, the combustion pattern is classified as Gr.0 andGr.1. When a range of b₂>120 kPa, the combustion pattern is classifiedas Gr.3. When a range of 20≦b₂≦120, the combustion pattern is classifiedas Gr.2.

Additionally, since this engine shows a tendency in which θ_(MBF)0.3 toθ_(MBF)0.7 decrease together with b₂ until b₂ reaches 120 kPa, both ofthe ignition delay and the combustion duration become short. On theother hand, if b₂ exceeds 120 kPa, there is a tendency in whichθ_(MBF)0.3 and θ_(MBF)0.5 decreases, but θ_(MBF)0.7 increase instead. Ina region where b₂ exceeds 120 kPa, it can be determined that theignition delay becomes short, but the combustion duration becomes long.

Next, cases of the third to fifth harmonic waves will be described withreference to FIGS. 10 to 12.

FIGS. 10 to 12 are view showing analysis results regarding theamplitudes of the third to fifth harmonic waves at the start time,respectively. Incidentally, in the case of IMEP, it can be confirmedthat there is a correlation depending on the components of thefundamental wave and the secondary harmonic wave (refer to JapaneseUnexamined Patent Application, First Publication No. 2010-261370D). Thethird to fifth harmonic wave components to be described here hardly haveany influence on the value of IMEP.

On the other hand, in the case of MBF timing θ_(MBF), as shown in theaforementioned FIGS. 8 and 9, when the order is low (in the case of thefundamental wave and the secondary harmonic wave), a range (particularlyGr.3) where the polygonal line graph of the MBF timing θ_(MBF) overlapsa lump is produced.

Moreover, the amplitudes of the third to fifth harmonic waves areanalyzed regarding the MBF timing θ_(MBF). As a result, when the orderis low, it can be understood that, in the range (particularly Gr.3)where the polygonal line graphs of the MBF timing θ_(MBF) overlap thelump, the relationship between b_(k) and θ_(MBF) becomes clear as theorder of the harmonic waves is increased from 3 to 5, and mutualcorrelation is easily distinguished.

Additionally, the classification of the combustion patterns according tothe magnitude of b₃ to b₅ is also allowed by the same method as b₂.

As shown in the above-described FIGS. 8 to 12, a clear proportionalrelationship is recognized between the amplitude b_(k) of the harmonicwaves and the MBF timing θ_(MBF). Detection of the MBF timing θ_(MBF) isallowed by operation processing based on this proportional relationshipwithout depending on means called the combustion analysis.

(Influence that Harmonic Wave Order k Has on Correlation with MBF Timingθ_(MBF))

Any influence that the harmonic wave order k has on the correlation withthe MBF timing θ_(MBF) will be described with reference to FIG. 13. FIG.13 is a view showing the correlation between the harmonic wave order kand the MBF timing θ_(MBF) at the start time. FIG. 13 shows thecorrelation between two cases including a case where a correlationcoefficient is only combustion pattern Gr.2, and a case where Gr.2 andGr.3 are combined. The correlation between the harmonic wave order k andthe MBF timing θ_(MBF) is generally higher in the case of only Gr.2.Additionally, respective correlation coefficients between the harmonicwave order k, and θ_(MBF)0.3 and θ_(MBF)0.5 show values nearer −1 than−0.9 in a range where k is 2 to 5, and show a strong negativecorrelation. Additionally, when the order is a fourth order (k=4), thecorrelation coefficient shows −0.99 and shows the strongest negativecorrelation. The reason why the correlation becomes weak in the case ofθ_(MBF)0.7 is because the value of θ_(MBF)0.7 tends to change fromdecrease to increase in a region where the value of b_(k) is large. Thistendency causes deterioration of linearity.

As shown above, there is a high correlation between the amplitudes b₂ tob₅ of the secondary to fifth harmonic wave components included in thecylinder pressure waveform with the rotational frequency of thecrankshaft as the fundamental frequency and the timings (θ_(MBF)0.3,θ_(MBF)0.5, θ_(MBF)0.7) at which MBF becomes 30%, 50%, and 70%.Additionally, the classification of the combustion patterns, that is,the patterns of the heat release rate and the mass burn fraction, isallowed depending on the magnitude of the amplitudes of the respectiveharmonic wave components.

The combustion characteristics at the start time are shown in theabove-described embodiment.

[Study of Combustion Characteristics When Acceleration/DecelerationOperation is Performed]

Subsequently, the combustion characteristics obtained when the engineperforms an acceleration/deceleration operation will be described withreference to FIGS. 14 to 38.

The characteristics of the patterns of the heat release rate and themass burn fraction are arranged to clarify the relationship with theWiebe function through the same method as that at the time of theaforementioned start (reference materials: “Fuel Injection andCombustion of Diesel Engine” written by Gyorgy Sitkei (joint-translatedby Tameo Tsubouchi and Kiyoo Kato), Asakura Bookstore).

Moreover, a method of estimating MBF0.5 timing without using thetechnique called the combustion analysis is shown by observing themagnitude of the amplitudes of the secondary to fifth harmonic wavecomponents included in the cylinder pressure waveform.

Hereinafter, a description will be made according to the aforementionedorder.

(Comparison with Identification Result by Wiebe Function of MBFCalculation Value)

Even when the engine performs an acceleration/deceleration operation,the aforementioned Expressions (2) to (5) are considered to be similarat the start time. Moreover, the MBF calculation value by Expression (5)can be approximated according to the expression of the Wiebe functionshown in the following Expressions (6).

$\begin{matrix}\left\lbrack {{Expression}\mspace{11mu} 7} \right\rbrack & \; \\{{{MBF}_{W} = {1 - {\exp \left( {- {ax}^{({m + 1})}} \right)}}}{{{where}\mspace{14mu} x} = \frac{\theta - \theta_{s}}{\theta_{e} - \theta_{s}}}} & (6)\end{matrix}$

a, m: Coefficients of Wiebe function

θ: Arbitrary crank angle during combustion duration

θs, θe: Crank angle of ignition and combustion end

In addition, when the MBF calculation value according to Expression (5)is expressed in the form of Expression (6), a timing at whichMBF_(W)=0.999 is regarded as combustion end timing (x=1), and a=6.908 isobtained.

First, a verification experiment performed for describing the principlein the present embodiment will be described. A general-purposefour-cycle engine is used for this verification experiment. In varioustypes of measurement shown below, an acceleration/deceleration operationis performed while the rotation speed NE (crank rotation speed) of thecrankshaft 11 is 900 rpm to 2400 rpm by changing the opening degree ofthe throttle valve 18 up to ¼ to ¾.

The cylinder pressure is measured in continuous 300 cycles at intervalsof 1 deg. CA in synchronization with the crankshaft rotation angle bythe pressure sensor (not shown) and the charge amplifier (not shown)that are provided at the combustion chamber 8 for the experiment. Therespective amounts shown in the previous Expressions (2) to (6) areobtained from the measured cylinder pressure P. Here, the maximumcylinder pressure P_(max), and the crank angles θ_(Pmax) and θ_(MBF) arecalculated by the secondary interpolation from values at every 1 deg.CA.

(Changes in P_(max), θ_(Pmax), and IMEP in Acceleration/DecelerationOperation)

FIG. 14 is a view showing P_(max), θ_(Pmax), and IMEP calculated fromthe cylinder pressure measured during the acceleration/decelerationoperation. FIG. 14 shows changes in P_(max), θ_(Pmax), and IMEP whileCycle Nos. 78 to 236 equivalent to about 2 cycles of theacceleration/deceleration operation are extracted from the cylinderpressure measured in the continuous 300 cycles. In FIG. 14, Ac, Cs, andDe represent the rough ranges of operation periods for acceleration,constant speed, and deceleration. The acceleration operation duration Acshows a duration in which an acceleration operation is performed inwhich the rotating speed is increasing from 900 rpm to 2400 rpm bysetting the throttle opening degree from ¼ to ¾. The constant-speedoperation duration Cs shows duration in which a constant speed operationadjusted so that the throttle opening degree is ¾ and the rotating speedbecomes approximately constant at 2400 rpm is performed. Thedeceleration operation duration De shows duration in which adeceleration operation is performed in which the rotating speed isdecreased from 2400 rpm to 900 rpm by changing the throttle openingdegree from ¾ to ¼.

From FIG. 14, IMEP, P_(max), and θ_(Pmax) increase gradually in theacceleration operation duration Ac. If entry into the constant-speedoperation duration Cs is allowed, P_(max) declines and fluctuated with acertain width together with IMEP and θ_(Pmax). In the decelerationoperation duration De, these tend to decrease while fluctuating.

In the following, Cycle Nos. 78 to 86, Nos. 87 to 110, and Nos. 111 to137 are mainly selected, respectively, as analyzed targets of theoperation periods for acceleration, constant speed, and deceleration,from a total range (Cycle Nos. 78 to 137) including the operationperiods for acceleration, constant speed, and deceleration.

(Changes in Cylinder Pressure, Heat Release Rate, and MBF DuringAcceleration/Deceleration Operation Duration)

Changes in the ignition delay, the combustion duration, and IMEP duringthe acceleration/deceleration operation duration will be described withreference to FIGS. 15 to 18.

FIG. 15 is a view showing the changes in the ignition delay, thecombustion duration, and IMEP during the acceleration/decelerationoperation duration. From FIG. 15, the ignition delay and the combustionduration show the same change tendency when the acceleration or constantspeed operation is performed, and there is a tendency in which thecombustion duration becomes short if the ignition delay (time) becomessmall, however, in contrast, the combustion duration also becomes longif the ignition delay (time) becomes large. If entry into thedeceleration operation is allowed, the combustion duration is longparticularly when the fluctuation of IMEP is large.

FIG. 16 is a view showing the results obtained when the cylinderpressure P, HR, and MBF in a complete cycle during the accelerationoperation duration are overwritten. As are shown in FIG. 16, there is atendency in which P_(max) and HR_(max) begin to increase as the numbersof cycles are overlapped and the crank angle position θ_(HRmax) at thetime of HR_(max) approaches TDC.

FIG. 17 is a view showing the results obtained when the cylinderpressure P, HR, and MBF in the complete cycle during the constant-speedoperation duration are overwritten. As shown in FIG. 17, if entry intothe constant-speed operation duration is allowed, the fluctuation of HRis recognized, but the patterns thereof are approximately the same.

FIG. 18 is a view showing the results obtained when the cylinderpressure P, HR, and MBF in the complete cycle during the decelerationoperation duration are overwritten. As shown in FIG. 18, in thedeceleration operation duration, fluctuations in P, HR, and MBF arelarge, and a cycle in which two-peak combustion having two peaks in Poccurs can also be seen.

(Relation between Grouping of Combustion Patterns and Operational State)

The relationship between the grouping of the combustion patterns and anoperational state will be described with reference to FIGS. 19 to 23.The groups of the combustion patterns during theacceleration/deceleration operation including constant speed areclassified from the shape of the above cylinder pressure waveform andthe above waveforms of HR and MBF. The combustion patterns aredetermined by the same method as the aforementioned method at the starttime.

FIG. 19 is a view showing a combustion pattern in which two peaks (peakvalues) can be observed in the cylinder pressure P. The combustionpattern shown in FIG. 19 is classified as a combustion pattern of Group11 (hereinafter referred to as Gr.11).

FIG. 20 is a view showing a combustion pattern in which fluctuations inpatterns of the cylinder pressure waveform, the heat release rate HR,and MBF are small and from which one peak (peak value) can be observedin HR. The combustion pattern shown in FIG. 20 is classified as acombustion pattern of Group 12 (hereinafter referred to as Gr.12).

FIG. 21 is a view showing a combustion pattern from which a flat portioncan be observed in the cylinder pressure P after TDC. The combustionpattern shown in FIG. 21 is classified as a combustion pattern thatappears when shift is made from Gr.11 to Gr.12, and is referred to as acombustion pattern of Group 12′ (hereinafter referred to as Gr.12′)herein. As for the combustion patterns under respective operatingconditions, the combustion pattern of only Gr.12 is observed in theacceleration operation duration, the combustion patterns of Gr.12 andGr12′ are observed in the constant-speed operation duration, and thecombustion patterns including all of Gr.11, Gr.12 and Gr.12′ areobserved in the deceleration operation duration.

Information on the combustion patterns classified herein is shown on thegraph (IMEP graph) showing a change in IMEP, which is shown in theaforementioned FIG. 15. In the acceleration operation duration Ac, onlythe combustion pattern of Gr.12 (double circle) is shown, and in theconstant-speed operation duration Cs, the combustion pattern of Gr.12′(filled circle) is shown at valley portions of the IMEP graph and thecombustion pattern of Gr.12 (double circle) are shown at the otherportions. Additionally, in the deceleration operation duration De, thefraction of the combustion pattern of Gr.12′ (filled circle) increases,and the combustion pattern of Gr.11 (open circle) is shown at valleyportions where the value of IMEP declines greatly.

Here, the results obtained when the mass burn fraction MBF isapproximately identified by the Wiebe function regarding theabove-described three combustion patterns (Gr.11, Gr.12, and Gr.12′)will be described with reference to FIG. 22.

FIG. 22 is a view showing the results obtained when the mass burnfraction MBF is approximately identified by the Wiebe function. Althougha slight difference is recognized between the calculation value MBFaccording to Expression (5) and MBF_(w) approximated to the Wiebefunction in the region of MBF>0.9 from FIG. 22, these coincide with eachother well in the other regions. Additionally, since a residualsum-of-squares R² is equal to or less than 0.02, it can be understoodthat the accuracy of approximation to the illustrated Wiebe function isalso excellent. Additionally, in the case of the example shown in FIG.22, m (coefficient of Wiebe function)=1.48 in the combustion patternGr.11, m=0.63 in the combustion pattern Gr.2, and m becomes anintermediate value (m=1.10) between both in the combustion patternGr.12′. It can be understood from these that the magnitude of thecoefficient m of the Wiebe function has any influence on a peak valueHR_(max) of the heat release rate, and if m becomes large, HR_(max)decreases.

Next, the relationship between the coefficient m of the above-mentionedWiebe function, and crank angles θ_(MBF)0.3, θ_(MBF)0.5, and θ_(MBF)0.7at which the mass burn fraction MBF of Expression (5) shows 30%, 50%,and 70% will be described with reference to FIG. 23.

FIG. 23 is a view showing the relationship between a coefficient m ofthe above-mentioned Wiebe function, and crank angles θ_(MBF)0.3,θ_(MBF)0.5, and θ_(MBF)0.7 at which the mass burn fraction MBF ofExpression (5) shows 30%, 50%, and 70%. It can be confirmed from FIG. 23that θ_(MBF)0.3, θ_(MBF)0.5, and θ_(MBF)0.7 increase together with m.Additionally, as mentioned above, when a case where m is small is thecombustion pattern Gr.12, a case where m is large is the combustionpattern Gr.11, and a case where m is an intermediate value between bothis the combustion pattern Gr.12′, it is possible to approximately groupthe combustion patterns from the magnitude of m. However, as shown, itcan be seen that the variations are large.

(Method of Estimating Mass Burn Fraction 50% Timing)

As mentioned above, according to Expression (2), IMEP is obtained fromthe amplitudes b₁ and b₂ of the frequency components of one or twotimes, using the rotational frequency of the crankshaft included in thecylinder pressure waveform as the fundamental frequency. Additionally,it is confirmed that an excellent correlation is established between theamplitudes b₂ to b₅ of the higher harmonic waves, and the MBF timing(θ_(MBF)0.3, θ_(MBF)0.5, and θ_(MBF)0.7) by deriving even the amplitudesb₃ to b₅ of the third to fifth higher harmonic waves in addition tothese frequency components as described as the case at the start time.

Hereinafter, the same study will be tried with reference to FIGS. 24 and25.

FIG. 24 is a view showing the relationship between the fundamental waveamplitude b₁ (horizontal axis) of the first item of the right-hand sideof the IMEP operational expression (the aforementioned Expression (2)),and the MBF timing θ_(MBF) (vertical axis). Additionally, FIG. 25 is aview showing the relationship between the fundamental wave amplitude b₂(horizontal axis) of the second item of the right-hand side of the IMEPoperational expression (the aforementioned Expression (2)), and the MBFtiming θ_(MBF) (vertical axis).

The value of b₁ shown in FIG. 24 becomes large in the combustion patternGr.12 in which the peak value of the heat release rate HR is high, andbecomes small in Gr.11 in which the peak value is low. Although there isa tendency as a whole in which the MBF timing θ_(MBF) declines withrespect to an increase in b₁, variation is large similar to the case atthe start time.

Meanwhile, the degree of the correlation between b₂ and the MBF timingθ_(MBF), which is shown in FIG. 25, is excellent, and the possibility ofestimation of the MBF timing θ_(MBF) can be confirmed from the magnitudeof b₂. Additionally, the classification of the combustion patterns isalso allowed on the basis of the magnitude of b₂.

For example, two threshold values (10 kPa and 34 kPa) that determine themagnitude of b₂ are determined, and the groups of the combustionpatterns are determined on the basis of the magnitude of b₂. Accordingto this determination result, a case where b₂ is equal to or less thanabout 10 kPa is the combustion pattern Gr.11, a case where b₂ is equalto or more than about 34 kPa is the combustion pattern Gr.12, and a casewhere b₂ is an intermediate value between both is the combustion patternGr.12′.

Next, the analysis results regarding the amplitudes of the third tofifth harmonic waves will be described.

FIGS. 26 to 28 are views showing the analysis results regarding theamplitudes of the third to fifth harmonic waves, respectively.

The same study results regarding the amplitudes b₃ to b₅ of the third tofifth harmonic waves are shown in FIGS. 26 to 28. A tendency in whichthe combustion patterns Gr.11 Gr.12′ overlap each other with an increasein the harmonic wave order, and the portion of the combustion patternGr.12 extends laterally is the same as that of the case at the starttime.

If estimation of the MBF50% timing θ_(MBF)0.5 is allowed using theaforementioned relationship from the amplitudes b₂ to b₅ of thesecondary to fifth harmonic waves, the combustion analysis atcalculation intervals of about 1 deg. CA becomes unnecessary accordingto the aforementioned Expressions (4) and (5). Additionally, if b₂ canbe used as the second item of the right-hand side of the IMEPoperational expression (2) as an index, there is no need for a newoperation, and thus, it is convenient for a user.

To confirm this possibility, a correlation coefficient and slope areobtained regarding a case of Gr.11+Gr.12+Gr.12′ including all thecombustion patterns and a case of Gr.12+Gr.12′ excluding the combustionpattern Gr.11 from these combustion patters, from the relationshipsbetween the amplitude components b₁ to b₅ of the fundamental wave tofifth harmonic wave and the MBF timings θ_(MBF)0.3, θ_(MBF)0.5 andθ_(MBF)0.7, which are shown in FIGS. 24 to 28.

FIG. 29 is a view showing the correlation between the harmonic waveorder k during the acceleration/deceleration operation and the MBFtiming θ_(MBF).

Additionally, FIG. 30 is a view showing the slope of the MBF timingθ_(MBF) to the amplitudes of the frequency components during theacceleration/deceleration operation.

From FIG. 29, as for both of the combustion patterns Gr.11+Gr.12+Gr.12′,and Gr.12+Gr.12′, the correlation between b₂ and the MBF timingsθ_(MBF)0.3, θ_(MBF)0.5 and θ_(MBF)0.7 is the strongest compared to theother higher order, and the correlation coefficient is within a range ofnegative values −0.96 to −0.97. In b₃ to b₅ having higher order thansaid order, there is a tendency in which the correlation becomes weakwith an increase in the order.

However, in the case of Gr.12+Gr.12′, the correlation coefficientbecomes about −0.9 even in b₃ and b₄. Moreover, in the case ofGr.12+Gr.12′, the correlation with θ_(MBF)0.7 is lower compared to theothers.

Meanwhile, FIG. 30 shows the slope of the correlation. Since sensitivitybecomes higher as the slope is gentler when the MBF timing θ_(MBF)0.5 isestimated from the magnitude of b_(k), it is desirable that the absolutevalue of the slope be smaller. It can be confirmed from FIG. 30 that theslopes in b₂ and b₃ are the approximately same value, and if the orderbecomes larger than this value, the slope becomes steep.

The relationship between the amplitude b₂ of the secondary harmonic waveand the MBF timing θ_(MBF)0.5 at the time of theacceleration/deceleration operation and the start will be described withreference to FIG. 31. FIG. 31 is a view showing the relationship betweenthe amplitude b₂ of the secondary harmonic wave and the MBF timingθ_(MBF)0.5 at the time of the acceleration/deceleration operation andthe start. In FIG. 31, the results (Gr.11, Gr.12, and Gr.12′) at thetime of the acceleration/deceleration operation and the results (Gr.1,Gr.2, and Gr.3) at the start time are plotted on the same graph. Bothdata are detected in different engines, and two graphs do not overlapeach other, but can be approximated to straight lines or curved linesaccording to respective slopes. In addition, the combustion pattern Gr.3having two peaks in the heat release rate is not observed at the time ofthe acceleration/deceleration operation.

However, the variation width of b₂ to a pressure change in P_(max) showsan approximately equal value in both engines in the combustion patternGr.11 showing the same level of cylinder pressure as the motoringpressure.

Moreover, as the combustion patterns showing one heat release rate peak,the combustion patterns Gr.12 and Gr.12′ at the time of the decelerationoperation and the combustion patterns Gr.2 at the start time are theresults obtained from the different engines. However, in both of thecombustion patterns Gr.12 and Gr.12′ at the time of the decelerationoperation, and the combustion pattern Gr.2 at the start time, θ_(MBF)0.5decreases linearly with respect to an increase in b₂, and the tendencythereof becomes the same.

In this way, although the relationships between b₂ to b₅ and the MBFtiming θ_(MBF)0.5 are inherent in the respective engines, the pointsthat these relationships can be used as an index when the combustionpatterns are classified and can be used as an index when the MBF timingθ_(MBF)0.5 is estimated are common.

Application to control of engines of actual vehicles is allowed by usingthe amplitudes of harmonic waves up to about secondary to fifth order asthe indexes for the classification of the combustion patterns and theestimation of the MBF timing θ_(MBF)0.5.

This is because, in the case of an engine that is operated at a arotation speed NE of 6000 rpm, the secondary to fifth harmonic wavesbecome low-frequency components in a range of 200 to 500 Hz. As aresult, the desired value of the natural frequency of the sensor unit 16can be set to be low with respect to a cylinder pressure sensor thatdirectly measures the cylinder pressure.

Moreover, the number of data items, such as the cylinder pressure, to beused can be reduced in the specific calculation of b₂ to b₅ according toExpression (3). This contributes also to reduction of ECU operationload.

FIG. 32 is a view showing a case where the number n of data items, suchas the cylinder pressure, to be used is reduced in the calculation of b₂according to Expression (3). FIG. 32 shows the results when the numberof data items is reduced to n=72 of intervals of 10 deg. CA. When acalculation method up to now, that is, the method of performs operationaccording to Expressions (4) and (5), is used, as the data of thecylinder pressure, n=720 is required as the number of data items ofintervals 1 deg. CA. As shown in FIG. 32, the results when the number ofdata items is reduced to n=72 of intervals of 10 deg. CA are shown. FIG.32 approximately coincides with the results of the aforementioned FIG.25 obtained by calculating b₂ with the number of data items of theintervals of 1 deg. CA being n=720. Additionally, as for both of thecombustion patterns Gr.11+Gr.12+Gr.12′, and Gr.12+Gr.12′, thecorrelation coefficient between b₂ and the MBF timings θ_(MBF)0.3,θ_(MBF)0.5 and θ_(MBF)0.7 is within a range of negative values −0.96 to−0.97 and this correlation coefficient also becomes the approximatelysame value.

To summarize the above, the following results can be obtained.

(1) The approximate accuracy of MBF according to the Wiebe function withrespect to the combustion patterns Gr.11, Gr.12, and Gr.12′, whichappear at time of the acceleration/deceleration operation, is excellent.

(2) A proportional relationship is established between the amplitudes b₂to b₅ of the secondary to fifth harmonic waves included in the cylinderpressure waveform, and the MBF timings θ_(MBF)0.3, θ_(MBF)0.5, andθ_(MBF)0.7. It is believed from this that b₂ to b₅ are used as theindexes for the estimation of the MBF timings and the classifications ofthe combustion patterns. In the case of b₂, the correlation coefficientbecomes −0.96 to −0.97, and shows strong correlation. This value becomesapproximately the same even if the number of cylinder pressure dataitems during one cycle is reduced to n=72 of intervals of 10 deg. CA.

(3) Although the relationship between b₂ to b₅, and the MBF timingθ_(MBF) becomes inherent in engines with different specifications fromthe comparison between the results in the engines, the fact that bothare proportional is the same, and it is confirmed that the possibilityof the classification of the combustion patterns b₂ to b₅ and theestimation of the MBF timing θ_(MBF) is common. According to thistechnique, the combustion analysis of HR or the like becomesunnecessary.

As shown above, the principle of calculating the MBF timing θ_(MBF)without performed the combustion analysis has been described.

(Method of Estimating MBF Timing when S/N Ratio of Output Signal ofSensor is Poor)

A method of estimating the MBF timing in a case where the S/N ratio ofan output signal of a sensor is poor will be described with reference toFIG. 33. Here, the case where the S/N ratio of the output signal of thesensor is poor means a case where a signal to noise ratio (S/N ratio)becomes low when a component showing a change in the cylinder pressureincluded in an output signal of a sensor is defined as a signalcomponent (S component) and fluctuation components other than thecomponent showing the change in cylinder pressure are defined as a noisecomponent (N component).

FIG. 33 is a schematic view showing the positions of the sensors in thecylinder structure in the present embodiment. In FIG. 33, similar to theaforementioned FIG. 3, the positions of the respective sensors in thecylinder structure 2A are shown in a plan view as viewed from a cylinderhead 35 (35A) side with respect to the cylinder structure 2A. The samecomponents as those of the aforementioned FIG. 3 among the componentsshown in FIG. 33 will be designated by the same reference numerals.

The respective sensors can be simultaneously provided at a cylinder head35A in FIG. 33. Here, the results measured by sensors attached todifferent positions in the cylinder head 35A, different types ofsensors, or the like are compared.

For example, reference numeral 16 b designates a gap sensor, referencenumerals 26 a and 26 b designates acceleration sensors, referencenumeral 27 designates a pressure sensor that measures the cylinderpressure, and reference numeral 28 designates a load washer. Therespective sensors are provided in places that are easily influenced bythe vibration when the internal combustion engine 2A drives. Therefore,particularly the acceleration sensors 26 (26 a, 26 b) are easilyinfluenced by noise or disturbance. Additionally, an output signal ofthe pressure sensor 27 that directly measures cylinder pressure has aproblem of the zero drift that the offset value of a signal component (Scomponent) changes. In this way, even if any sensors are used, thesensors are influenced by noise, disturbance, or the like. Therefore,even when the S/N ratio of the output signal of a sensor is poor, it isdesired that the MBF timing θ_(MBF) can be calculated. Therefore, it isshown that the MBF timing θ_(MBF) can be calculated by a method shownbelow even when the S/N ratio of the output signal of the sensor ispoor.

The S/N ratios of output signals of the acceleration sensors 26 a and 26b are greatly influenced by the attachment positions of the sensors. Forexample, the S/N ratio of the output signal of the sensor at theattachment position of the acceleration sensor 26 b becomes poorer thanthat at the attachment position of the acceleration sensor 26 a in FIG.33.

Hereinafter, a procedure of calculating the MBF timing θ_(MBF) from anoutput signal of the acceleration sensor 26 b attached to the positionof the acceleration sensor 26 b in FIG. 33 so that the S/N ratio of theoutput signal of the sensor becomes intentionally poor will bedescribed. In addition, in FIG. 33, the position of the accelerationsensor 26 b is the vicinity of the intake valve 3 in the cylinder head35. However, it goes without saying that the invention can be applied toa case where the acceleration sensor is attached to positions other thanthe position of the sensor shown in FIG. 33 or to cases where differenttypes of sensors are used. For example, in FIG. 33, the pressure sensor27 directly measures the cylinder pressure. Therefore, excellentmeasurement results in which S/N ratio of an output signal of the sensoris high are obtained. Additionally, when the gap sensor is used, the S/Nratio of an output signal of the sensor at the attachment position ofthe gap sensor 16 a of FIG. 33 becomes better than that at theattachment position of the gap sensor 16 b of FIG. 33.

FIG. 34 is a view showing an example of combustion parameters indirectlymeasured from an output signal of the acceleration sensor 26 b (FIG. 33)and combustion parameters measured by the pressure sensor 27 (FIG. 33)by comparison. Changes in the combustion parameters (vertical axis) fromthe crank angle (horizontal axis) are shown in FIG. 34. In the verticalaxis of FIG. 34, the cylinder pressure P, HR, and MBF are shown as thecombustion parameters. Additionally, by showing the combustionparameters with any suffixes of “_ref” and “_acc” being attached to thecombustion parameters, respectively, the results measured by thepressure sensor 27 (FIG. 33) are shown as “ref”, and the resultsindirectly measured from output signals of the acceleration sensor 26 b(FIG. 33) are shown as “acc”.

In the cylinder pressure P shown in FIG. 34, a peak of a cylinderpressure (p_acc) indirectly measured from an output signal of theacceleration sensor 26 b is observed near a maximum cylinder pressureP_(max) of a cylinder pressure (p_ref) measured by the pressure sensor27. Additionally, it can be understood that a change in the cylinderpressure (p_acc) indirectly measured from the output signal of theacceleration sensor 26 b resembles a change in the cylinder pressure(p_ref) measured by the pressure sensor 27, in terms of overalltendency, but the level of noise or disturbance superimposed on thesignal is quite large with respect to a main signal component.

Therefore, by applying the aforementioned Expression (2) using theamplitude of a low-pass frequency component regarding IMEP, an excellentresult in which a correlation coefficient ρ is (ρ>0.98) is obtained. Onthe other hand, a large error is caused if the maximum cylinder pressureP_(max), and the crank angle θ_(pmax) at which the maximum cylinderpressure P_(max) is obtained are directly obtained from the same outputwaveform.

Therefore, monitoring of P_(max) and θ_(pmax) is performed according tothe amplitude b₂ of the secondary harmonic wave of the second item ofthe right-hand side in Expression (2), and the phase φ₂ thereof

FIG. 35 is a view showing the relationship between the amplitude b₂ ofthe secondary harmonic wave and the maximum cylinder pressure P_(max).The result is illustrated in FIG. 35 that a proportional relationship ispresent between the amplitude b₂ of a harmonic wave in an outputwaveform of the acceleration sensor, and P_(max) by the output of thepressure sensor, and the correlation coefficient ρ becomes (ρ>0.98).

Additionally, when the relationship of θ_(pma), with the phase φ₂ of thesecondary harmonic wave is investigated, variation is present, but thecorrelation coefficient ρ thereof is (ρ=−0.756), and a proportionalrelationship can be confirmed. In this way, by using the amplitude andphase of the harmonic wave included in the output waveform of theacceleration sensor, it is possible to perform monitoring with higheraccuracy than directly obtaining P_(max) and θ_(pmax) from the outputsignal of the acceleration sensor shown in FIG. 34.

Meanwhile, in the combustion analysis, it is necessary to performdifferential operation in addition to signal processing, such asatmospheric pressure location and pressure conversion. When a largedisturbance or noise is overlapped on a signal waveform, the analysisbecomes more difficult.

Thus, MBF can be estimated by function-approximating the relationshipbetween the amplitude b_(k) of the higher harmonic waves included in theoutput waveform of the acceleration sensor, and the MBF timing θ_(MBF)and by reversely operating the parameters of the Wiebe function ofExpression (6) on the basis of this function-approximation.

As described earlier, since a=6.908 is obtained by regarding the timingat which MBF_(W)=0.999 as the combustion end timing (x=1) in Expression(6), the three remaining unknowns m, θ_(s), and θ_(e) are calculatedfrom the relationship between three arbitrary MBF and crank angles(MBF₁, θ_(MBF1)), (MBF₂, θ_(MBF2)), and (MBF₃, θ_(MBF3)). Theaforementioned three arbitrary MBF and crank angles are estimated fromthe amplitude b_(k) (k is order) of the higher harmonic waves includedin the waveform of the acceleration sensor.

Although the aforementioned three arbitrary MBF and crank angles (MBF₁,θ_(MBF1)), (MBF₂, θ_(MBF2)), and (MBF₃, θ_(MBF3)) are not particularlylimited, for example, MBF timings θ_(MBF) at which MBF becomes 0.05,0.25, and 0.80, respectively, are preferable.

The relationship between the amplitude b₂ of the secondary harmonic waveincluded in the output waveform of the acceleration sensor, andθ_(MBF0.05), θ_(MBF0.25), and θ_(MBF0.80) obtained by the output of thepressure sensor will be described with reference to FIG. 36. FIG. 36 isa view showing the relationship between the amplitude b₂ of thesecondary harmonic wave included in the output waveform of theacceleration sensor, and θ_(MBF0.05), θ_(MBF0.25), and θ_(MBF0.80)obtained by the output of the pressure sensor. The graph shown in FIG.36 is given by simultaneously performing the results of the cylinderpressure measured in advance by the pressure sensor 27, and thedetection of the cylinder pressure calculated from an output signal ofan external sensor (here, the acceleration sensor 26 b), and obtaining arelational expression θ_(MBF)=f(b₂) between θ_(MBF) obtained by thepressure sensor 27 and the amplitude b₂ of the secondary harmonic wavein the waveform of the external sensor.

Although the order of the amplitude b_(k) of the higher harmonic wavesincluded in the output signal of the acceleration sensor 26 b is notparticularly limited, if the order is the second order (k=2), acorrelation becomes relatively excellent in broad operating conditions,and b₂ may be obtained in an IMEP calculation process. When b₂ isobtained in the IMEP calculation process in this way, it is preferableto share the operation result of b₂, thereby making individualcalculation of b₂ unnecessary.

Here, if the relationship between b₂ and θ_(MBF) is approximated by asecondary expression, conversion is made as in Expression (7).

[Expression 8]

θ_(MBF0.25)=2.0848(b ₂)²−13.305b ₂+20.993

θ_(MBF0.25)=2.7233(b ₂)²−18.116b ₂+36.955

θ_(MBF0.80)=6.2799(b ₂)²−42.623b₂+97.109  (7)

According to the approximate expression of the above Expression (7),θ_(MBF0.05), θ_(MBF0.25), and θ_(MBF0.80) are estimated from the valueof b₂, and the unknowns m, θ_(s), and θ_(e) of the Wiebe function arecalculated from these values. Additionally, the estimation value(MBF_acc) of MBF of the respective MBF timings can be obtained from theapproximate expression of MBF shown in the aforementioned Expression(6).

The relationship between MBF and the crank angle θ obtained as mentionedabove is shown in the aforementioned FIG. 34. In FIG. 34, (MBF_acc)coincides with (MBF_ret) obtained from the output signal of the pressuresensor 27 well except for the ignition timing. Additionally, it can beunderstood that a heat release rate equalizing value (HR_acc) calculatedby differentiating (MBF_acc) shows the tendency of a change similar tothe heat release rate (HR_ref) obtained from the output signal of thepressure sensor 27.

By applying the detecting method of the present embodiment, themeasurement of the cylinder pressure by the pressure sensor 27 becomesunnecessary. Additionally, the estimation of MBF, the MBF timing, andthe heat release patterns HR is allowed even when the S/N ratio of theoutput signal of the external sensor is poor and it is difficult todirectly perform the combustion analysis.

Additionally, according to the detecting method of the presentembodiment, the types of the sensors are not limited to the accelerationsensor, the force sensor, the gap sensor, or the like, and can also beapplied to the pressure sensor that directly measures the cylinderpressure. For example, in the output signal of the pressure sensor, evenwhen the zero drift of the output signal of the sensor occurs due tothermal influence, even when pressure conversion is difficult, or thelike, detection can be made without being influenced by these.Advantageous effects can be exhibited by the detecting method of thepresent embodiment.

In this section, the description regarding the method of determiningvariables θ_(s), θ_(c), and m in the expression of the Wiebe functionshown in the aforementioned Expression (6) will be supplemented.

Expression (6) shown earlier is modified to obtain Expression (8). Inaddition, a in Expression (8) is a fixed number (for example, a=6.908)as mentioned above.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 9} \right\rbrack & \; \\{{\log \left\lbrack \frac{- {\ln \left( {1 - {MBF}_{W}} \right)}}{a} \right\rbrack} = {\left( {m + 1} \right){\log \left( \frac{\theta - \theta_{s}}{\theta_{e} - \theta_{s}} \right)}}} & (8)\end{matrix}$

Now, three known points arranged on an MBF pattern (curved line) aredetermined, and the coordinates thereof are represented by (MBF₁,θ_(MBF1)), (MBF₂, θ_(MBF2)), and (MBF₃, θ_(MBF3)). These are substitutedin the aforementioned Expression (8), respectively, and expressionsshowing in Expression (9) to Expression (11) are obtained, respectively.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 10} \right\rbrack & \; \\{A_{1} = {{\log \left\lbrack \frac{- {\ln \left( {1 - {MBF}_{1}} \right)}}{a} \right\rbrack} = {\left( {m + 1} \right){\log \left( \frac{\theta_{{MBF}\; 1} - \theta_{s}}{\theta_{e} - \theta_{s}} \right)}}}} & (9) \\\left\lbrack {{Expression}\mspace{14mu} 11} \right\rbrack & \; \\{A_{2} = {{\log \left\lbrack \frac{- {\ln \left( {1 - {MBF}_{2}} \right)}}{a} \right\rbrack} = {\left( {m + 1} \right){\log \left( \frac{\theta_{{MBF}\; 2} - \theta_{s}}{\theta_{e} - \theta_{s}} \right)}}}} & (10) \\\left\lbrack {{Expression}\mspace{14mu} 12} \right\rbrack & \; \\{A_{3} = {{\log \left\lbrack \frac{- {\ln \left( {1 - {MBF}_{3}} \right)}}{a} \right\rbrack} = {\left( {m + 1} \right){\log \left( \frac{\theta_{{MBF}\; 3} - \theta_{s}}{\theta_{e} - \theta_{s}} \right)}}}} & (11)\end{matrix}$

Additionally, the relationships shown in Expression (9) to Expression(11) are arranged to obtain Expression (12).

$\begin{matrix}\left\lbrack {{Expression}\mspace{11mu} 13} \right\rbrack & \; \\{Z = {\frac{A_{1} - A_{2}}{A_{2} - A_{3}} = {\frac{\log \left( \frac{\theta_{{MBF}\; 1} - \theta_{s}}{\theta_{{MBF}\; 2} - \theta_{s}} \right)}{\log \left( \frac{\theta_{{MBF}\; 2} - \theta_{s}}{\theta_{{MBF}\; 3} - \theta_{s}} \right)} = \frac{\log \left( \frac{\theta_{{MBF}\; 1} - \theta_{s}}{\theta_{{MBF}\; 2} - \theta_{s}} \right)}{\log \left( \frac{\theta_{{MBF}\; 2} - \theta_{s}}{\theta_{{MBF}\; 3} - \theta_{s}} \right)}}}} & (12)\end{matrix}$

Moreover, the following Expression (13) is derived by modifyingExpression (12).

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 14} \right\rbrack & \; \\{\left( \frac{\theta_{{MBF}\; 2} - \theta_{s}}{\theta_{{MBF}\; 3} - \theta_{s}} \right)^{Z} = \left( \frac{\theta_{{MBF}\; 1} - \theta_{s}}{\theta_{{MBF}\; 2} - \theta_{s}} \right)} & (13)\end{matrix}$

Since the unknown in Expression (13) is only θ_(s), θ_(s) can beobtained by solving this expression.

Meanwhile, as for θ_(c) and m, θ_(c) and m can be obtained according toExpression (14) by solving Expression (9) and Expression (10).

[Expression 15]

θ_(e)=θ_(s)+10 ^(d)  (14)

In addition, d in Expression (14) is shown in Expression (15).

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 16} \right\rbrack & \; \\{d = \frac{{A_{1}{\log \left( {\theta_{{MBF}\; 2} - \theta_{2}} \right)}} - {A_{2}{\log \left( {\theta_{{MBF}\; 1} - \theta_{s}} \right)}}}{A_{1} - A_{2}}} & (15)\end{matrix}$

Additionally, as shown in Expression (16), m can be obtained accordingto Expression (9).

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 17} \right\rbrack & \; \\{m = {{A_{1}/{\log \left( \frac{\theta_{{MBF}\; 1} - \theta_{s}}{\theta_{e} - \theta_{s}} \right)}} - 1}} & (16)\end{matrix}$

In this way, θ_(e) and m can be uniquely calculated if θ_(s) isdetermined. Hence, a method of calculating θ_(s) becomes important. Inthe following description, study is added to this point.

As is clear from Expression (13) shown earlier, whether this expressionbecomes a linear equation or a nonlinear equation is determineddepending on the value of an exponent Z. For example, in the case ofZ=1, this expression becomes a linear equation, and θ_(s) is requiredfrom a simple algebraic equation. In contrast, in the case of Z≠1,Expression (13) becomes a nonlinear equation. Even if Expression (13) isa nonlinear equation, in Z=2, that is, a case where Expression (13) isarranged and becomes a secondary equation regarding θ_(s) and in Z=3,that is, a case where Expression (13) is arranged and becomes a thirdequation regarding θ_(s), a solution can be obtained by applying aquadratic formula or a cubic formula. Additionally, in the case ofZ=0.5, as will be described below, the expression is arranged and becomea secondary equation regarding θ_(s). Thus, a solution can be obtainedby applying a quadratic formula similarly. In this way, in Expression(13), it is difficult to obtain θ_(s) except for special cases, such asZ=2, Z=0.5, or Z=3. Since it is difficult to obtain a solution in casesother than Z=2, Z=0.5, or Z=3, for example, it is necessary to apply theNewton Raphson method or the like, and perform at least several repeatedcalculations to calculate θ_(s) numerically. Execution of this operationin real time on board causes an increase in the operation load in ECU.

Also to improve the response of control, it is desirable to make theoperation load of ECU as light as possible in the calculation of θ_(s).For this purpose, it is necessary to determine three points where thevalues of A₁, A₂, and A₃ of Expression (9) to Expression (11) thatdetermine the value of Z is calculated, that is, in three points (MBF₁,θ_(MBF1)), (MBF₂, θ_(MBF2)), and (MBF₃, θ_(MBF3)) that are shown asknown points so that the conditions of Z=1, 2, 0.5, and 3 to beanalytically solved by Expression (13) are satisfied. In the following,calculation expressions of θ_(s) when Z takes the above-describedvalues, and the relationships (selecting methods) of the known threepoints that satisfy the calculation expressions are clarified.

i) In the case of Z=1

In the case of Z=1, Expression (13) becomes a linear equation regardingθ_(s), and θ_(s) is obtained by the following Expression (17).

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 18} \right\rbrack & \; \\{\theta_{s} = \frac{\theta_{{MBF}\; 2}^{2} - {\theta_{{MBF}\; 1}\theta_{{MBF}\; 3}}}{{2\theta_{{MBF}\; 2}} - \theta_{{MBF}\; 1} - \theta_{{MBF}\; 3}}} & (17)\end{matrix}$

Additionally, the relationship of the known three points that satisfyZ=1 becomes the following Expression (18) if the conditions of the knownthree points that satisfy Z=1 are obtained from Expression (9),Expression (10), and Expression (12).

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 19} \right\rbrack & \; \\{{{MBF}_{1} = {1 - {\exp \left\lbrack \frac{\ln^{2}\left( {1 - {MBF}_{2}} \right)}{\ln \left( {1 - {MBF}_{3}} \right)} \right\rbrack}}},{or},{{MBF}_{3} = {1 - {\exp \left\lbrack \frac{\ln^{2}\left( {1 - {MBF}_{2}} \right)}{\ln \left( {1 - {MBF}_{1}} \right)} \right\rbrack}}}} & (18)\end{matrix}$

ii) In the case of Z=2

In the case of Z=2, Expression (13) becomes a secondary equationregarding θ_(s) shown in Expression (19).

[Expression 20]

Aθ _(s) ² −Bθ _(s) +C=0  (19)

In addition, in Expression (19), A, B, and C are as shown in Expression(20), respectively.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 21} \right\rbrack & \; \\\left. \begin{matrix}{A = {{3\theta_{{MBF}\; 2}} - \theta_{{MBF}\; 1} - {2\theta_{{MBF}\; 3}}}} \\{B = {{3\theta_{{MBF}\; 2}^{2}} - {2\theta_{{MBF}\; 1}\theta_{{MBF}\; 3}} - \theta_{{MBF}\; 3}^{2}}} \\{C = {\theta_{{MBF}\; 2}^{3} - {\theta_{{MBF}\; 1}^{2}\theta_{{MBF}\; 3}^{2}}}}\end{matrix} \right\} & (20)\end{matrix}$

θ_(s) can be obtained as Expression (21) by adopting a value near thecombustion TDC (θ=0) from the root of the secondary equation of theabove-described Expression (19) as θ_(s).

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 22} \right\rbrack & \; \\{\theta_{s} = {\frac{1}{2A}\left\lbrack {B - \sqrt{B^{2} - {4A\; C}}} \right\rbrack}} & (21)\end{matrix}$

Additionally, the relationship of the known three points that satisfyZ=2 becomes the following Expression (22) from Expression (9),Expression (10), and Expression (12).

$\begin{matrix}{\mspace{20mu} \left\lbrack {{Expression}\mspace{14mu} 23} \right\rbrack} & \; \\{{MBF}_{1} = {{1 - {\exp \left\lbrack {- \frac{\left\{ {- {\ln\left( {1 - {MBF}_{2}} \right\}}} \right\}^{3}}{\left\{ {- {\ln\left( {1 - {MBF}_{3}} \right\}}} \right\}^{2}}} \right\rbrack}} = {1 - {\exp \left\lbrack \frac{\ln^{3}\left( {1 - {MBF}_{2}} \right)}{\ln^{2}\left( {1 - {MBF}_{3}} \right)} \right\rbrack}}}} & (22)\end{matrix}$

In addition, in the case of Z=2, the combination of MBF=0.06, MBF=0.50,and MBF=0.90 is allowed, and the estimation of an MBF pattern throughMBF=0.50 is allowed.

iii) In the case of Z=0.5

In the case of Z=0.5, Expression (13) becomes a secondary equationregarding θ_(s) shown in Expression (23), similar to the case of Z=2.

[Expression 24]

Aθ _(s) ² −Bθ _(s) +C=0  (23)

In addition, in Expression (23), A, B, and C are as shown in Expression(24), respectively.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 25} \right\rbrack & \; \\\left. \begin{matrix}{A = {{3\theta_{{MBF}\; 2}} - \theta_{{MBF}\; 1} - {2\theta_{{MBF}\; 3}}}} \\{B = {{3\theta_{{MBF}\; 2}^{2}} - {2\theta_{{MBF}\; 1}\theta_{{MBF}\; 3}} - \theta_{{MBF}\; 1}^{2}}} \\{C = {\theta_{{MBF}\; 2}^{3} - {\theta_{{MBF}\; 1}^{2}\theta_{{MBF}\; 3}}}}\end{matrix} \right\} & (24)\end{matrix}$

Similar to the case of Z=2, θ_(s) can be obtained as Expression (25) byadopting a value near the combustion TDC (θ=0) from the root of thesecondary equation of the above-described Expression (23) as θ_(s).

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 26} \right\rbrack & \; \\{\theta_{s} = {\frac{1}{2A}\left\lbrack {B - \sqrt{B^{2} - {4A\; C}}} \right\rbrack}} & (25)\end{matrix}$

Additionally, if the conditions of the known three points that satisfyZ=0.5 are obtained by Expression (9), Expression (10), and Expression(12), the following Expression (26) is obtained.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 27} \right\rbrack & \; \\{{MBF}_{1} = {1 - {\exp \left\lbrack {- \frac{\left\{ {- {\ln \left( {1 - {MBF}_{2}} \right)}} \right\}^{1.5}}{\left\{ {- {\ln \left( {1 - {MBF}_{3}} \right)}} \right\}^{0.5}}} \right\rbrack}}} & (26)\end{matrix}$

In addition, in the embodiment shown above, the rotational frequency ofthe crankshaft is used as the fundamental frequency. However, one cycle(a series of operation until the air-fuel mixture is taken into thecombustion chamber and is combusted and a combustion gas is exhaustedfrom the combustion chamber) of the internal combustion engine may beused as the fundamental frequency.

In that case, it is necessary to take into consideration that thecrankshaft make two rotations during one cycle in the case of afour-cycle engine (four-stroke engine), and the crankshaft makes onerotation during one cycle in the case of a two-cycle engine (two-strokeengine). Particularly, when one cycle of the internal combustion engineis adopted as the fundamental frequency in the four-cycle engine, it ispossible to calculate the MBF timing θ_(MBF), using secondary to tenthharmonic wave components of the fundamental frequency.

Additionally, the detailed description of the analysis method in thecalculation of MBF shown above is based on b_(k) obtained by expressingthe amplitude of the k-th harmonic wave with the total of the product ofthe cylinder pressure and the sine function as in the above Expression(3). Even in a case based on a_(k) obtained by expressing the amplitudeof the k-th harmonic wave with the total of the product of the cylinderpressure and the cosine function as in the above Expression (3)′ insteadof the above Expression (3), analysis can be performed similar to thecase based on the above b_(k).

The correlations between MBF as the results analyzed and obtained fromthe amplitude of the k-th harmonic wave and actual MBF may be differentin cases where analysis based on b_(k) derived from the sine function isperformed and analysis based on a_(k) derived from the cosine functionis performed, depending on the characteristics of the internalcombustion engine 2, and the kinds, positions, or the like of thesensors.

The correlations between MBF as the results analyzed and obtained fromthe amplitude of the k-th harmonic wave, and the actual MBF will bedescribed with reference to FIGS. 37 and 38.

FIG. 37 is a view showing the correlation between MBF obtained on thebasis of b_(k) derived from the sine function, and the actual MBF. FIG.37 shows a change in the correlation coefficient (vertical axis) betweenMBF obtained on the basis of b_(k) and the actual MBF, according to theorder k of b_(k) (horizontal axis), on the condition of the combinationbetween the values (θ_(MBF0.05), θ_(MBF0.25), and θ_(MBF0.80)) ofθ_(MBF) and the types (the cylinder pressure sensor (ref) and the gapsensor (gap)) of the sensors. According to the correlation coefficientshown in FIG. 37, it can be understood that the value of the correlationcoefficient shows (−0.9 to −1) in a range where the value of the order kis from 1.5 to 3.5, and the correlation is high.

FIG. 38 is a view showing the correlation between MBF obtained on thebasis of a_(k) derived from the cosine function, and the actual MBF.FIG. 38 shows a change in the correlation coefficient (vertical axis)between MBF obtained on the basis of a_(k) and the actual MBF, accordingto the order k of a_(k) (horizontal axis), on the condition of thecombination between the values (θ_(MBF0.05), θ_(MBF0.25), andθ_(MBF0.80)) of θ_(MBF) and the types (the cylinder pressure sensor(ref) and the gap sensor (gap)) of the sensors. According to thecorrelation coefficient shown in FIG. 38, it can be understood that thevalue of the correlation coefficient shows (−0.9 to −1) in a range wherethe value of the order k is from 0.5 to 1.5, and the correlation ishigh.

In this way, if the case of FIG. 37 is compared with the case of FIG.38, it can be understood that different tendencies are shown such thatthe ranges of the orders where the correlation becomes high aredifferent, and particularly regarding FIG. 38, the correlation becomeshigh even when a frequency lower than the frequency of the fundamentalwave is given and the degree k is 0.5.

[Processing in Engine Control Unit]

(Processing Performed by ECU 1 that Detects MBF Timing θ_(MBF))

Subsequently, the processing performed by the ECU 1 that detects the MBFtiming θ_(MBF) on the basis of the aforementioned principle will bedescribed.

The ECU 1 (detecting device) detects the combustion state of the engine2 (internal combustion engine) that transmits power via the crankshaft11.

The CPU 1 b (calculation unit) in the present embodiment calculates themass burn fraction MBF by detecting the crank angle, on the basis of thefrequency components included in the state change amount of the statechange of the cylinder structure 2A (detection target) according to achange in the cylinder pressure depending on the combustion cycle of theengine 2 and including the harmonic wave components of the fundamentalwave having the rotational frequency of the crankshaft 11 as thefundamental frequency.

The CPU 1 b (calculation unit) in the present embodiment calculates themass burn fraction MBF on the basis of the correlation between theharmonic wave components and the crank angle. The correlation betweenthe harmonic wave components and the crank angle is defined in advanceas operational expressions or tables in which information showingrelationships are stored, and is stored in the memory 1 c capable ofbeing referred to by the CPU 1 b (calculation unit). The CPU 1 b(calculation unit) calculates the mass burn fraction MBF according tothe above operational expressions or the above information stored in thetables.

The CPU 1 b (calculation unit) in the present embodiment calculates themass burn fraction MBF from a plurality of frequency components of thefrequency components corresponding to frequencies of natural numbermultiples of the fundamental frequency when the internal combustionengine 2 is a four-cycle engine as mentioned above.

For example, the CPU 1 b (calculation unit) may include the frequencycomponent (s) up to the fifth order of the fundamental wave as theharmonic wave components, in the frequency components included in thestate change amount of the state change. In other words, the CPU 1 b(calculation unit) may include at least one of the frequency componentsup to the fifth order of the fundamental wave as the harmonic wavecomponent. For example, the CPU 1 b (calculation unit) may include atleast one of the frequency components of the secondary order, the thirdorder, the fourth order, and the fifth order of the fundamental wave asthe harmonic wave component. Additionally, for example, the CPU 1 b(calculation unit) may include both or any one of fourth and fifthfrequency components of the fundamental wave as the harmonic wavecomponents, in the frequency components included in the state changeamount of the state change.

In addition, the CPU 1 b (calculation unit) in the present embodimentcan calculate the mass burn fraction MBF from a plurality of frequencycomponents of the frequency components corresponding to frequencies of(natural number −0.5) multiples of the fundamental frequency, therebyperforming processing according to the same procedure as in the case ofthe four-cycle engine, when the internal combustion engine 2 is atwo-cycle engine. In short, any frequency group out of a frequency groupincluding frequencies of natural number multiples of the fundamentalfrequency according to the rotation speed of the crankshaft 11 per onecombustion cycle of the internal combustion engine 2 and a frequencygroup including frequencies of (natural number −0.5) multiples of thefundamental frequency is determined. The CPU 1 b (calculation unit) canperform the above processing on the basis of a plurality of frequencycomponents among the frequency components corresponding to thefrequencies included in the determined frequency group.

Additionally, the CPU 1 b (calculation unit) in the present embodimentdefines an expression showing a combustion model in which the combustioncycle of the internal combustion engine 2 is modeled. The expressionshowing the combustion model includes, as variables, a first crank angleaccording to the timing of ignition in the combustion cycle of theinternal combustion engine 2, a second crank angle according to thetiming of combustion end in the combustion cycle, a third arbitrarycrank angle, and a mass burn fraction according to the third crankangle. The CPU 1 b (calculation unit) calculates the mass burn fractionon the basis of the expression showing the combustion model.

Additionally, in the CPU 1 b (calculation unit) in the presentembodiment, combustion model coefficients showing the combustion modelare included in elements of the expression showing the combustion model,and the combustion model coefficients are obtained on the basis ofinformation on a plurality of known sets that are arbitrarily selectedamong information on sets of crank angles and mass burn fractionsaccording to the crank angles. The CPU 1 b (calculation unit) calculatesthe mass burn fraction according to the expression showing thecombustion model, which is an operational expression including, aselements, the combustion model coefficients obtained on the basis of theinformation on the plurality of selected known sets.

Additionally, in the CPU 1 b (calculation unit) in the presentembodiment, to make the operation load of calculating the mass burnfraction light, with respect to the relationship between the respectivecrank angles (θ_(MBF1), θ_(MBF2), and θ_(MBF3)) included in the threeknown sets and the crank angle θ_(s) according to the timing of theignition, the plurality of known sets are selected so that Z ofExpression (13) become any one of 0.5, 1, 2 and 3. The CPU 1 b(calculation unit) calculates the mass burn fraction according to theexpression showing the combustion model, which is obtained on the basisof the information on the plurality of known sets selected in that way.

In this way, the ECU 1 in the present embodiment detects the combustionstate of the engine 2 (internal combustion engine) on the basis of thecrank angle at which the calculated mass burn fraction MBF is obtained.

(Procedure of Processing of ECU 1 that Detects MBF Timing θ_(MBF))

Subsequently, the specific procedures of the processing of the ECU 1that detects the MBF timing θ_(MBF) on the basis of the aforementionedprinciple will be described.

(Procedure 1) As shown in the above principle of the present invention,the basic characteristics of the engine 2 as a detection target aredetected in advance, and the information according to the basiccharacteristics is stored in the ECU 1 (memory 1 c). Information,including the information that determines conversion factors referred toin Procedure 4.5 to be described below, and operation conditions (aselection condition for selecting order, a weighted condition ofweighted calculation, or the like) referred to in Procedure 4.5, areincluded as the information stored in the ECU 1.

(Procedure 2) The sensor unit 16 detects the state change amount of thestate change of the cylinder structure 2A (detection target) accordingto a change in the cylinder pressure depending on the combustion cycleof the engine 2, and sends the state change amount to the ECU 1.

(Procedure 3) The ECU 1 performs input processing (including A/Dconversion processing) of the state change amount of the aforementionedstate change sent from the sensor unit 16, and stores the result.Procedure 3 is continuously and repeatedly performed on the basis of apredetermined cycle.

(Procedure 4) The ECU 1 calculates the mass burn fraction MBF or the MBFtiming θ_(MBF) on the basis of the state change amount of the statechange sent from the sensor unit 16. In addition, the operationprocessing in Procedure 4 is performed by the CPU 1 b of the ECU 1.Additionally, Procedure 4 can be subdivided into a plurality ofprocessing items shown below.

(Procedure 4.1) The ECU 1 calculates the rotation speed NE of thecrankshaft 11.

(Procedure 4.2) The ECU 1 calculates the rotational frequency of thecrankshaft 11 (crankshaft) according to the rotation speed NE.

(Procedure 4.3) The ECU 1 extracts the harmonic wave components of thefundamental wave from the frequency components included in the statechange amount of the state change, on the basis of the calculatedrotational frequency (fundamental frequency) of the crankshaft 11(crankshaft) (refer to Expression (3)).

(Procedure 4.4) The ECU 1 calculates the amplitude information (forexample, b1 to b5) on the frequency components including the harmonicwave components of the fundamental wave having the rotational frequencyof the crankshaft 11 (crankshaft) as the fundamental frequency, from thestate change amount of the aforementioned state change stored in theaforementioned Procedure 3.

(Procedure 4.5) The ECU 1 calculates the mass burn fraction MBF on thebasis of the amplitude information (for example, b1 to b5) on thefrequency components including the harmonic wave components calculatedin the aforementioned Procedure 4.4, and the conversion factors storedin the aforementioned Procedure 1.

For example, the ECU 1 subjects the amplitude information on the orderselected among the amplitude information (for example, b1 to b5) on thefrequency components including the harmonic wave components calculatedin the aforementioned Procedure 4.4 to conversion processing accordingto a linear operational expression or a curvilinear approximateexpression determined by conversion factors according to the selectedorder, thereby calculating the mass burn fraction MBF.

Alternatively, the ECU 1 converts the amplitude information (forexample, b1 to b5) on the frequency components including the harmonicwave components calculated in the aforementioned Procedure 4.4,according to a linear operational expression or a curvilinearapproximate expression determined by conversion factors according to anorder, respectively, and subjects the respective conversion results tothe weighted processing, thereby calculating the mass burn fraction MBF.

Additionally, the ECU 1 may calculate the MBF timing θ_(MBF) from themass burn fraction MBF calculated according to the above procedures.

(Procedure 5) The EUC 1 outputs the mass burn fraction MBF or the MBFtiming θ_(MBF) calculated in the aforementioned Procedure 4 as a statevariable. Additionally, the EUC 1 performs the control required for acontrolled target that adjusts the operational state of the engine 2 onthe basis of the calculated mass burn fraction MBF or MBF timing θ_(MBF)as the state variable.

Here, after the processing of Procedure 5 is finished, the EUC 1repeatedly perform the processing from Procedure 4. In addition, theprocessing of Procedure 3 is performed in parallel to the processing ofProcedure 4 and Procedure 5.

(Control of Engine Based on Mass Burn Fraction MBF)

Subsequently, the control of the engine 2 performed as processing of theabove Procedure 5 will be described. The control shown below is shown asan example.

The ECU 1 (CPU1 b) in the present embodiment controls the internalcombustion engine that transmits power via the crankshaft. According tothe calculated mass burn fraction, the mass burn fraction according tothe detected crank angle (the duration in which the mass burn fractionbecomes a predetermined range) or the like according to the detectedcrank angle, the ECU 1 (CPU 1 b) can control the operational state ofthe engine 2. The control of the combustion state of the engine 2 basedon the mass burn fraction includes the control of the ignition timing,the control of the fuel injection timing, the control of the exhaust gasrecirculation processing, or the like.

(1) In Case of Ignition Timing Control

For example, the ECU 1 may calculate a desired ignition timing on thebasis of a crank angle measured by an angle sensor, and the calculatedmass burn fraction (refers to the Japanese Unexamined PatentApplication, First Publication No. H7-180645).

The above desired ignition timing is calculated by a relationalexpression of Y=aX+b. Here, Y is ignition timing represented by a crankangle to the top dead center. X is a difference between a crank angle inan arbitrary reference mass burn fraction of fuel injected into acylinder, and a crank angle in an arbitrary mass burn fraction in astage in which combustion has proceeded. A and b are fixed numbersdetermined depending on the characteristics of a spark ignition engineincluding the ignition plug 9.

(2) In Case of Fuel Injection Timing Control

For example, the ECU 1 calculates a combustion duration θ50-90equivalent to the duration of 50% to 90% of the mass burn fraction. Thecombustion duration 050-90 and a reference value θ (reference) arecompared, and it is determined whether or not there is a deviation equalto or greater than a predetermined value between the newest combustionduration θ50-90 (θ (present)) and the reference value θ (reference).

When the deviation equal to or greater than a predetermined value isbetween the newest combustion duration θ50-90 (θ (present)) and thereference value θ (reference) as the result of the above determination,the ECU 1 corrects the injection timing. When the newest combustionduration θ50-90 is greater than the reference value θ (reference), theECU 1 repeats advance correction of the injection timing until thecombustion duration θ50-90 does not change in a decreasing direction. Onthe other hand, when the newest combustion duration 050-90 is equal toor less than the reference value θ (reference), the ECU 1 repeats retardcorrection of the injection timing until the combustion duration θ50-90begins to change in an increasing direction (for details, refer toJapanese Unexamined Patent Application, First Publication No.2000-8928).

(3) When Control of Exhaust Gas Recirculation Processing (EGRProcessing) is Performed

The EGR 22 returns a portion of exhaust gas to the intake system, andmaintains a suitable combustion state.

For example, the ECU 1 can detect the combustion state from thecalculated mass burn fraction.

As an example, one or more sensors are used to measure the amount of theexhaust gas that flows in through the EGR 22. For example, since intakeair oxygen concentration may be directly related to EGR adjusted withrespect to exhaust gas oxygen concentration, the control of the amountof EGR may be performed on the basis of the intake air oxygenconcentration or the mass burn fraction.

Additionally, as an example, the EGE 22 may include an exhaust gassensor, an exhaust gas temperature sensor, an exhaust gas pressuresensor, or the like. In some examples, the sensors that the EGR 22 hasmay include, for example, one or more sensors to be used to measure theamount of EGR. The amount of EGR, for example, may be controlled on thebasis of the mass burn fraction and/or the intake air oxygenconcentration.

As described above, the ECU 1 of the present embodiment can detect thecrank angle without using a special pressure sensor to thereby easilycalculate the mass burn fraction (MBF). Additionally, the ECU 1 of thepresent embodiment can easily detect the crank angle θ_(MBF), at which apredetermined mass burn fraction (MBF) is obtained, without measuringthe cylinder pressure. Accordingly, an expensive pressure sensor isunnecessary, reliability can also be enhanced, and application to theengine 2 to be mounted on a vehicle becomes easy.

Additionally, the ECU 1 can control the combustion state of the engine2, on the basis of the detection value (calculation value) of the crankangle θ_(MBF) at which a predetermined mass burn fraction (MBF) isobtained, and realize low fuel consumption and clean exhaust gas.

Additionally, the ECU 1 can detect the crank angle through the sameprocessing without using a special pressure sensor to thereby easilycalculate the mass burn fraction (MBF) while the engine 2 reaches thesteady operation from the start thereof or when theacceleration/deceleration operation is performed. Additionally, the ECU1 of the present embodiment can easily calculate the crank angleθ_(MBF), at which a predetermined mass burn fraction (MBF) is obtained,similar to the above case.

Additionally, the relationships among the maximum cylinder pressure andits crank angle, the indicated mean effective pressure, the heat releaserate, and the mass burn fraction (MBF) are clarified from theexperimental results shown in the present embodiment. Accordingly, theECU 1 can calculate the crank angle θ_(MBF), at which a predeterminedmass burn fraction (MBF) is obtained, through the operation processingof the same method as the calculation method of the indicated meaneffective pressure. In short, the ECU 1 can sharing the results of theprocessing without individually performing different kinds of operationprocessing, to thereby finish common processing at one time, and thiscan contribute to a decrease in the amount of operation processing to beperformed by the ECU 1.

Additionally, in the present embodiment, the MBF timing θ_(MBF) iscalculated using a glass engine for experiments and a general-purposefour-cycle gasoline engine. However, the invention is not limited tothese. For example, the invention can also be applied to a two-cyclegasoline engine, a diesel engine, and a rotary engine.

Additionally, in the present embodiment, the calculation of the MBFtiming θ_(MBF) is described in the case of a mechanism using thecrankshaft as a mechanism that converts the reciprocating motion of apiston into a rotational motion of a shaft. However, the invention isnot limited to these. The invention can also be applied to othermechanisms that convert the reciprocating motion of the piston into therotational motion of the shaft, for example, a crosshead mechanism, ascotch yoke mechanism, a Ross-York mechanism, a Rhombic mechanism, aswash plate mechanism, and the like.

Additionally, the above-described ECU 1 may make the programs forrealizing the respective functions recorded on computer-readablerecording media, and make the programs recorded on this recording mediaread into and executed in a computer system, to thereby perform theprocessing of the above-described respective sections, respectively. Inaddition, the term “computer system” herein includes OS or hardware suchas peripheral devices.

Additionally, if the “computer system” uses a WWW system, the computersystems also include a homepage-providing environment (or displayenvironment).

Additionally, the term “computer-readable recording media” mean portablemedia, such as a flexible disk, a magnetic-optical disk, ROM, andCD-ROM, and storage devices, such as a hard disk, built in the computersystem. Moreover, the term “computer-readable recording media” includesrecording media that dynamically hold the programs in a short time, likecommunication lines in cases where the programs are transmitted vianetworks, such as the Internet, or communication lines, such as atelephone line, or recording media that hold the programs during acertain period of time, like a volatile memory inside the computersystem serving as a server or a client in that case. Moreover, the aboveprograms may be programs for realizing some of the aforementionedfunctions, and may be programs that can realize the aforementionedfunctions in combination with the programs already recorded on thecomputer system.

Although the embodiment of the invention was described above in detailwith reference to the drawings, the specific configuration is notlimited to the embodiment, and design or the like that does not departfrom the scope of the invention are also included.

INDUSTRIAL APPLICABILITY

The ECU 1 (detecting device) shown in the present embodiment can detectthe crank angle without using a special pressure sensor to therebyeasily calculate the mass burn fraction MBF. Accordingly, the ECU 1(detecting device) can constitute a detecting device that detects thecombustion state in the internal combustion engine 2 mounted on, forexample, a vehicle or the like.

Additionally, the ECU 1 (detecting device) can control the internalcombustion engine 2 according to the information based on the detectedresults.

Additionally, in movable bodies (for example, a vehicle, a vessel, orthe like) including the ECU 1 (detecting device) shown in the presentembodiment, and the internal combustion engine 2, the ECU 1 (detectingdevice) can be appropriately controlled according to the combustionstate of the internal combustion engine 2.

What is claimed is:
 1. A detecting device that detects a combustionstate of an internal combustion engine that transmits power via acrankshaft, the detecting device comprising: a calculation unit thatcalculates a mass burn fraction by detecting a crank angle, on the basisof a frequency component showing a state change amount of a state changeof a detection target according to a change in a cylinder pressuredepending on a combustion cycle of the engine, and including a harmonicwave component of a fundamental wave of the frequency component.
 2. Thedetecting device according to claim 1, wherein the frequency componentshowing the state change amount of the state change of the detectiontarget is a frequency component including a harmonic wave component of afundamental wave having a rotational frequency of the crankshaft as afundamental frequency.
 3. The detecting device according to claim 1,wherein the calculation unit calculates the mass burn fraction on thebasis of a correlation between the harmonic wave component and the crankangle.
 4. The detecting device according to claim 1 wherein thecalculation unit calculates the mass burn fraction, using, as thefrequency component, a plurality of frequency components among frequencycomponents corresponding to frequencies of natural number multiples ofthe fundamental frequency or frequencies of (natural number −0.5)multiples of the fundamental frequency.
 5. The detecting deviceaccording to claim 4, wherein the calculation unit determines anyfrequency group out of a frequency group including frequencies ofnatural number multiples of the fundamental frequency according to arotation speed of the crankshaft per one combustion cycle of the engineor a frequency group including frequencies of (natural number −0.5)multiples of the fundamental frequency, and calculates the mass burnfraction, using, as the frequency component, frequency componentscorresponding to a plurality of frequencies among frequency componentscorresponding to the frequencies included in the determined frequencygroup.
 6. The detecting device according to claim 1, wherein thecalculation unit includes at least one of the frequency components up tothe fifth order of the fundamental wave as the harmonic wave component.7. The detecting device according to claim 1, wherein the calculationunit includes fourth and fifth frequency components of the fundamentalwave as the harmonic wave component.
 8. The detecting device accordingto claim 1, wherein the calculation unit calculates the mass burnfraction on the basis of an expression showing a combustion modelobtained by modeling the combustion cycle of the engine, and including,as variables: a first crank angle according to a timing of ignition inthe combustion cycle of the engine, a second crank angle according to atiming of combustion end in the combustion cycle; a third arbitrarycrank angle; and a mass burn fraction according to the third crankangle.
 9. The detecting device according to claim 8, wherein acombustion model coefficient inherent in the combustion model isincluded in an element of the expression showing the combustion model,and the combustion model coefficient is obtained on the basis ofinformation on a plurality of known sets that are arbitrarily selectedamong information on sets of crank angles and mass burn fractionsaccording to the crank angles, and wherein the calculation unitcalculates the mass burn fraction according to the expression showingthe combustion model that is an operational expression including thecombustion model coefficient in the element.
 10. The detecting deviceaccording to claim 9, wherein the plurality of known sets that arearbitrarily selected are three sets, wherein a relationship between therespective crank angles of the three sets, and the first crank angleaccording to the timing of the ignition is represented by Expression(1), and wherein the plurality of known sets are selected so that therelationship between Z of Expression (1) becomes any of 0.5, or 1, 2 and3 $\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 1} \right\rbrack & \; \\{\left( \frac{\theta_{{MBF}\; 2} - \theta_{s}}{\theta_{{MBF}\; 3} - \theta_{s}} \right)^{Z} = \left( \frac{\theta_{{MBF}\; 1} - \theta_{s}}{\theta_{{MBF}\; 2} - \theta_{s}} \right)} & (1)\end{matrix}$ θ_(MBF1), θ_(MBF2), and θ_(MBF3): Crank angles thatconstitute a set of an arbitrary crank angle and a mass burn fractionaccording to the crank angle are given in three different sets; θ_(s):First crank angle according to the timing of ignition.
 11. The detectingdevice according to claim 1, further comprising: a control unit thatcontrols an operational state of the internal combustion engine on thebasis of the calculated mass burn fraction.
 12. A detecting method thatdetects a combustion state of an internal combustion engine thattransmits power via a crankshaft, the detecting method comprising: aprocess of calculating a mass burn fraction by detecting a crank angle,on the basis of a frequency component showing a state change amount of astate change of a detection target according to a change in a cylinderpressure depending on a combustion cycle of the engine, and including aharmonic wave component of a fundamental wave of the frequencycomponent.